IN another period of enforced recuperation, aggreviated back injury, following my holiday to the pyrenees in May I am spending more time on the road and some firetracks paths, I cannot ride a skinny due to neck and back issues but would a 29er be a good compromise to build up as a bit quicker bike on roads and allow me to do some gentle paths?
What do people reckon?

How about a flat bar CX bike.

I'd be the first person to heartily recommend one but they are still mountain bikes, with what would generally be a similar position to what you ought to have on a 26" wheeled bike. Perhaps you ought to look at a hybrid if a more upright position and easygoing ride is what you're after?