If you're going to do Venice, Florence & Rome (which I think is a very good itinerary for a first trip), you definitely don't want a car. You obviously can't use one in Venice and don't want one in either Florence or Rome. Take the train between cities.

DH and I took a Globus tour last summer to Italy that was very nice. It is called Leisurely Italy and includes 3 days in Rome, 3 days in Tuscany(Florence 1 day) and 3 days in Venice.We did go to Rome 2 days early on our own and that than gave us 5 days in Rome. We loved this tour as there was as there was a lot of free time if you wanted to do some things on your own.I do enjoy having the hotels and transportation taken care of when visiting a country where I don't speak the language. When we go back though I imagine we will go on our own.

We took the "independent" tour I mentioned earlier just for the very reason that it allowed us a lot of free time to explore on our own. And, at the same time, it freed us of the worry, etc., about booking hotels, trains, etc.
Our first time also included Rome, Florence and Venice, and like letsgo39, we booked two extra days in Rome at the start of our trip.
And, as previous recommended, you definitely do NOT want to rent a car if you plan on making the big three Italian cities your itinerary.

Italy is very easy to do on your own for your overall trip. If you feel the need for a pro tour, you can find a day or half day tour in those cities. the nice thing about going on your own is that you can control the pace.

You DO NOt want a car for a trip to Rome, Florence and Venice. the train works much better and is much less hassle.

If you have at least nine nights I would divide them evenly between the three. If 10 or 11, I'd add time to Rome. 12 and I'd split evenly again.

Most places that you will stay have some form of online booking. there is a great deal of info and help on the internet in forums like these. So very easy to do on your own.

Based on so many of your recommendations, we have already made a couple of decisions regarding our trip to Italy. We definitely would like to do Rome, Florence and Venice for our first trip. If we decide to try and put this trip together on our own, we will not be renting a car but will, instead, use rail service, as well as cab service if and when necessary.
LETSGO39: Did you arrange your own flights to Rome and then join the Globus tour when you got there?
HOWARDR: Great suggestion!
My husband feels as though he is a "computer widower" because I've been spending hours on it researching the trip. My mind is actually getting boggled with all the information that is out there and I think I will take a break from it until after the Christmas holiday! However, as I make progress, I will keep you posted.

travel472, as I previously wrote, the "independent" tour type really gave us a lot of free time. Though our package included a half-day tour in each of the three cities, we opted not to take the one in Florence, and instead, went off on our own. And, our extra two days in Rome at the start of the experience afforded the opportunity to go to Pompeii, which was one of the highlights of that trip.
I cannot emphasize enough how much signing up for this basic package eased--and just about eliminated--our nervousness due this being our first trip to Italy.
Did we see everything during the 13 days of the trip? No. Did we have a great time? Yes. Did we return to Italy? Yes, two more times.....and we still haven't seen everything....not even close. And, by the way, on our two followup trips to Italy and one to Paris, we did all the planning and made all the arrangements ourselves.

Now that some of you have piqued my interest in, perhaps, arranging most of our Italy trip ourselves, did you find that booking your own hotels, flights, tours, etc. ahead of time was less expensive than going through a tour operator and having everything done for us?
Also, would it be in our best interest to use our Visa card or would it be better to pay for everything in cash?
Thank you!

"would it be in our best interest to use our Visa card or would it be better to pay for everything in cash?"

Depends on the cards - there are several threads here about that. I now travel with a Capital One Visa card - it's the only one I know about that doesn't charge a foreign conversion fee - in fact I get cash back. My Citibank cards charge a 3% conversion fee. Check with your bank to see what fees it will charge for using your ATM card to get cash (forget travelers' checks). Mine charges a 1% conversion fee, so I'm better off using the Visa card, but a lot smaller places don't take cards.

I get more satisfaction out of a trip I've booked myself. (Well, actually we only went on a tour once, the first time we went to Europe. After that, we figured we could do it ourselves. And have.) But you need to like doing research. For me, researching and anticipating is one of the best parts of the trip.

You can get lots of help online, here at Fodors and at www.tripadvisor.com and www.venere.com (for hotels). You've already found Slow Travel.

We look for small hotels with lots of local flavor, very centrally located. If you go on a tour, they book you in some big streamlined modern hotel not so conveniently located.

On our own, we walk a lot and enjoy the sights as we walk along. We pick the sights we want to see and get to stay there as long a time as we wish. And we don't spend any time sitting on a bus waiting for some tardy tour member.

We often go on local walking tours to get more expertise on what we're seeing.

With your mobility problems, you might have to look for local small bus tours to get around. Or even hire a taxi to give you a mini-tour. There's a website with help for mobility-impaired travelers. I couldn't find it with a quick google, but maybe somebody else has the URL.