Swim diapers??

C

My son is 7 months and in size 3 diapers. He’s real tall but pretty skinny! Anyways, I’m looking online at target and the pampers swim diapers come in a S, M, or L...which size should I get?!

Also, do y’all like the Baby Bum sunscreen? I’ve never had him actually outside in the sun for a long period of time so any advice would be greatly appreciated! We’re going to the lake for a few hours next week so I want to make sure I’m prepared.