When is it okay to bring LO to swim? Need thermal swimwear? Waterproof diapers? Where to get it? Thanks

I brought my LO to baby spa when he was 10weeks old. N when he turned 4 months I brought him to public pool. Currently 7 months and he goes for a swim at least once weekly. I usually let him wear double layer if he has not poo for the day. - disposable (Huggies ) + reusable ( moomookow) if not will be just the reusable layer I got him his swim wear from Fox which cost less than $30 but is not thermal material