Oriental Spa (not Oriental Palm - same group but different target customer base. Think Lexus vs. Toyota) in Tst is probably the closest you will get to the quality and ambiance in the big spas in SZ. It's probably the most expensive right now (Twice might be able confirm if there are any places dearer), Sauna de Palais was quite pricey too but for the size can't beat it.
Basic massage will set you back 1.5K with tips and if you spend time with all the other services like beauticians, can easily spend 3-4k a session.
Ask for a younger, good looking massusse from the managers and be brave to ask the lady after the flip. Most she can say no... but you'd have to be darn'ed ugly.