The Heath is good but you'll need to keep your eye on the time as public transport closes down and you might get stuck there!
The Vault naked nights (Monday and Thursday) are excellent. Be there at around or just before 7pm as, especially on Thursday, it gets busy.
Also try the Bunker on City Road ( nearest tube Old Street). They have themed nights so look at their website to see what floats your boat.
Also try SBN (tube Vauxhall) on Sunday afternoons. It starts at 2pm but I tend to arrive just after that as it gets busy as the afternoon goes on. Its basically wall to wall cock and hole.
You might look at Hardon to see if one of their monthly events falls on the week you're in town.
If you're adventurous and can face South London try the Lord Clyde. Nearest main line station is Deptford and then about 15 minute walk. It's newish. I've been a couple of times and had fun on one of those visits. They don't have website. Look them and others on squirt.irg
Saunas...are a but so-so. Sailor's, Locker Room, Pleasuredrome...all can be good or lousy. Can't easily say whats best day/time.
Good hunting. Let me know if you want more info or are looking for a hole to fill
John