You make the classic mistake of confusing Senso in Silom with Ssense in Suan Plu. You donโt go to Senso for the massage. Their massage skills are average. However, if you want a very decent to a very good massage (with extras if you want) you can go to Ssense.
An alternative in Sukhumvit, that is rarely mentioned here, is Kino-saki spa. Look out for Kensei.
If you are strictly after massage only you can go to the Prime massage in Silom.