In Pattaya, View Talay Villas all have (small) private swimming pools. You can book a one bedroom villa with pool. Their rates are somewhat expensive and they don't do well on Tripadvisor, but for sure you and your friend can splash about to your hearts' content. I used to own a house there specifically because I wanted to have some fun in/around the pool. There's no ID check so you and your friend can come and go as you please.