Pls help looking for a spa/other with a heated salt etc cleaned pool in the Sussex area (4 lengths)

Hi, I'm urgently seeking a non/v. low-chlorine swimming pool within spa/hotel/club/therapy centre etc. where I can swim proper lengths (doesn't need to be Olympic length tho!) for rehabilitating after health challenges, sea too cold and chlorine v bad for me. Poss to join spa/club just for swimming, don't need fancy trimmings/ or overnight (not rich!) just use of pool to be honest, where it wouldn't disturb people who are just relaxing etc. (altho not up to swimming Butterfly at present tbh!) I live in Hove, UK but willing to travel pref no further than London. Many many thanks, Catriona :)