Think of a spa in Phuket as the card you play when the weather rewrites the plan. Boat tours and beaches are the first to wobble in rain, so do not separate the spa day and the outdoor day from the start.
If you travel with children, match the age rule first. Kim's and Yarey use ages 3 to 11, Let's Relax at Veranda 6 to 11 and Divana ANDA 10 to 14, so the younger the child, the sooner you should check the waiting option.
Put venues with an early last booking in the morning or daytime and later ones in an evening pushed back by rain. Orientala at Deevana Patong Resort lasts to 17:30, Yarey has a separate 12:30 morning cutoff and Deep Relax Phuket books until 21:30.
In the rainy season, travel is also a cost. Kata Rocks is in Kata, Divana ANDA and Deep Relax are in the Laguna and Cherngtalay area and Kim's and Veranda are in Phuket Town, so choose near your hotel and then compare room layouts.