I was in KL in February this year, my experiences are covered in another thread
https://www.ukpunting.com/index.php?topic=450714.0but to summarise
Tinder/Bumble worked really well for me so you could easily get an overnighter in my opinion
Alternatively, just sit in one of the window seats in the Pacific bar on Changkat Butak Bintang at night and watch the girls that are working outside. They will all come inside and chat to you and make you an offer.
For your Spa fun, try Genesis Sauna Spa, also in Bukat Bintang - just google if for the address........it's easily walkable from your apartment, no more than 5 minutes. It's on one of the floors of an office block.
Hope that helps and look forward to reading your experiences.