You've got to do whatever works for you and makes life easier.
don't beat yourself up about it - just think of all those disposibles youve saved from landfil up till now.
changing a toddler 10 times a day is hard work! plus all the clothes youve got to wash because of leaks - so if I was going through this I think i'd do the same!
does sound like he's close to PT - ive know quite a few babies, who start flooding nappies just prior to PT!
I'm sure youve tried everything - but sometimes the flooding is occuring because the fabric cannot absorb the vast amount of wee fast enough! bamboo is classic for this because its super absorbant - but slow absorbing!
have your tried microfibre tops to the boosters - this is low absorbancy but fast! so works well ontop of @tanya