Staying in Sukhumvit gives you the widest choice. A Spa & Massage Bangkok (Sukhumvit 18) has good access around Asok and a broad programme range, which makes it easy to slot into an evening. Manjai massage carries a high review count and is worth noting when weighing price against access.
For a more composed spa setting, compare Divana Virtue Spa and Bhawa Spa on the 8. Both run longer programmes that assume a reservation, which suits giving one holiday evening over to a spa entirely. Diora Bangkok Langsuan pairs well with plans around Lumpini and Langsuan.
For an established brand with a settled programme, Oasis Spa Bangkok Sukhumvit 31 is worth considering. Its garden villa layout creates a quiet atmosphere inside the city, and fixed programme lengths make scheduling easy to calculate. THANN SANCTUARY SPA at the Emporium shopping complex sits inside a mall, so it attaches directly to a shopping afternoon.
For a different kind of rest with family, look at Yunomori Onsen & Spa Bangkok (Sukhumvit 26), which combines bathing facilities with massage. It is undemanding with older parents and works as an indoor alternative on a wet afternoon. Check bathing facility rules and any tattoo-related guidance in advance.
Before booking, confirm programme duration and price, how to reserve and when to arrive, couple or private room availability, shower facilities, tipping practice and the cancellation window. Evening slots fill first during this holiday, so book as soon as your dates are fixed, and treat the current product details as the final reference.