I love spa days, and so do the rest of the family, including several who are clinically obese.
My first visit was courtesy of Gransnet - I won a prize for a mother and daughter day at a spa near Newark, still outstandingly my favourite spa. DD is on the large size and has no worries at all about cavorting around in a swimming costume.
I might add at every spa I have visited the clientele could be described as a cross section of the female population found in any supermarket. All sizes, all shapes, plus a number of men - including DH, another whale, who also loves spas.
When we go to spas We go entirely for the water play we rarely have treatments, we have tried them, but they just do nothing for us. - and the food. Several spas have got knocked off our list because the food was more mass catering than haute cuisine.
I would rather have fewer spa days and pay more to have a truly luxurious experience and lovely food, than go more frequently and compromise on facilities. Quality over quantity every time.