I use the washable-reusable-swim nappies from www.doubibou.com - they are excellent, and they last for 1 year or so depending upon how fast your child grows.
I also use the BadgerBalm sunblock, also from www.doubibou.com.
Regarding those SPF swim suits that offer more coverage, they aren't 100%, so I would still use good sunblock. I got some once at that market in ShamShuiPo that sells electronics...there was one small stall that had them - but who knows if they were real or not?? Stanley sometimes has them too, but in larger sizes, again, not sure if they are real.