Rather than moving around more, I'd add nights to one or both of the places you are already going. If you have enough time and you have the interest, a side trip to Central Java to see Borobudor and Prambanam would be a nice accompianment.

i agree with kathie, esp at ubud..

look at alam shanti in ubud...

I agree that two bases is wise. You can get anywhere from either and a third might reduce travel time by no more than 1 hour except if you wanted to spend a few days in West Bali.
You might add 2 days to your Ubud base. Keep in mind it does not have to be right in the city center, actually there is no real center but a few areas over 5+ miles that make up what I would refer to as Bali proper. I would not stay more than 8-9 miles out of shopping district, just as a point of reference, because of the traffic. It could take 30 minutes to go that distance in high traffic/commuter hours. A driver/guide for several days is wise a good one like Putu also referred to as "Balifriend" costs about $60 for 10 hours. Just make sure he is taking you and not his cousin who is not as experienced. Putu has been a guide for 19 years and has excellent English.
Java, Central Java, is well worth 2-3 full days if you have the time and budget and it is only a 1 hour flight for ~$150 RT. We have used an excellent guide who is highly educated with very good English to explain the meaning of the 3 amazing temples, far more interesting than those in Bali in our opinion, some ways of living in small villages that are also quite interesting and a day trip to Dieng Plateau as or more beatiful than most scenery in Bali. He was able to get us discounts at hotels the 2 times we used his services.
He can be reached at: wiedyantara@hotmail.com
Enjoy!!