Not sure whether to drive up + stay overnight or do a day trip from Cairns where we'll be based still we start our sloow trek south down to Brisbane? Any recommendations?

Depends on how much time you have - Trek North has excellent guides which leave from Cairns for a day trip, but there's many accommodation options in Daintree area - see www.bnbnq.com.au - here you'll meet hosts who'll give you the best of local information.

MellyMel,
You could start your trip south by going north. After doing the Daintree, head up to the Atherton tablelands via the Rex Range. If you have time, side trips to chillagoe and Undara are worth it for the geology, caves and lava tubes. If you really mean sloow then allow a week one the tablelands as there is soo much to see and do.

On your way south, stop at The Boulders and Josephine Falls - just as good as Mossman Gorge and not nearly as crowded.

We did a day trip from Cairns ( had a rental car) and had a great time exploring the Daintree region.
We drove right up to Cape Tribulation, took a few bush walks, did a river cruise on the Daintree River and got back into Cairns about 7pm.

Have fun.

Agree with TreeRoo, it would be sad to head off down to Brisbane without taking in Atherton Tableland (sometimes marketed under Cairns Highlands) which unfortunately doesn't get much of a mention on this forum. There's some great accommodation options there too, once again see www.bnbnq.com.au

Thanks for the tips and yes, heading south to go north does sound like a good idea as does Undara Lava Tubes which I have seen advertised. We've got 21 days to enjoy Queensland and from previous trips we always regret leaving the North so early on. Whilst I'm here any advice on good places to stay in Cairns for a few days before we 'trek off'?

you could always try "Lilybank"

www.lilybank.com.au/

Hi we stayed at the Daintree eco lodge and loved it. I personally would reccomend staying at least one night in this area. We did the night hike through the eco lodge and it was fantastic. We liked it so much we went the next night too. We saw lots of wildlife that you don't see during the day. The night before we went they saw a python. Supposedly the best time to view wildlife at night is right after a full moon.