The Spa at Ritz-Carlton at Grande Lakes is nice. I've had some luck with "action" there, but of course, you have to be carful. Steam tends to be really hot, but dense enough that if you're at the far end no one can see in. Whirlpool is small enough where you can sit fairly close to someone to see if a leg or hand will brush against you. The showers are in a curved line around a corner, and it's easy enough to hang a towel over the glass door on one of the stalls at the end for more privacy, if you're sharing a shower.
Used to be the spa at Saratoga Springs (Disney) was good (lots of dads taking a break from the family), but they closed. The Grand Floridian Spa is small, but similarly good, with nice dads on display.