You have to let them learn to be dry.... and it sounds like hes ready to try so if i were you go for it!
If hes a 'wriggler' i find the washable bed pads move even more than the pampers bed mats!
Can i suggest you do waterprrof sheet, cotton sheet, bed mat, cotton sheet....
so then you just 'whip off' wet sheet and wet mat and are left with a dry sheet and waterproof undersheet just in case! *as suggested before
alternativly you could jeust get a couple of terrysheets with a water proof back and put one on top of the other, and just whip off the top wet one if it gets wet!
Dont be cross with him if hes wet... he HAS to learn!
My 4.5 year old charge (boy) stopped wearing his pull ups around febuary time... the 1st 3 nights he was dry, and then had a few consecutive nights of accidents...
they seem to have got mreo and more infrequent and in the past 4 weeks we have only had 1 accidnet... he was occasioanly waking up with a dry pull up (maybe twice a week max) but HE WANTED to give it a go... so mummy let him (half expecting after a week or 2 to go back to pull ups... but no hes been succesful 1st time!)
Good luck!