After 8 months of trying to figure this all out, my 5 yo DS has just has has first week of dry nights! So I feel your pain! Here's what I found worked - no guarantees for you little one, but hope you find it useful:
Don't use pull-ups for boys - they are useless because of night time erections - when willy goes up, wee goes everywhere - usually all over your sheets. I put DS back into nappies and it almost completely stopped all leakage and I went back to washing sheets only once a week. Being back in nappies certainly provided mine with a reason to want to get dry - he was pretty embarrassed about being a 'baby' in nappies!
I then went and bought a night time wetting alarm. NHS won't usually provide this for kids under 7, so go and buy one - they are expensive but you will eventually save money on nappies and washing costs - and you can sell it again on ebay once you've finished with it.
The alarm worked within 3 weeks. Initially, I put him in a pyjama top, a pair of underpants with the sensor over the material on his underpants, then covered the underpants with a disposable nappy. I slept in his bedroom and got him up and to the toilet every time the alarm went off. I only had to do this for 3 weeks.
I spent an extra week figuring out why little one was still laying in bed weeing himself, rather than getting up for the toilet. Fixed the night time lighting issue in the house and we haven't had an accident since.
Good luck - hope this helps!
I still use a waterproof plastic undersheet, in case of future accidents, but I totally recommend