Best Santorini 1/ day catamaran excursion

[budmeister]

I would like a 20 or so person max, often listed as semi private, with stops at   couple of beaches- not just near them, -swimming in hot springs, and enough seating for everyone.  

 

I have not found one where reviews either say all swimming is off boat or not enough seating. 

 

Have you a recommendation? 

I am 11 months out,  but caldera Yachting is full or unavailable my day and one popular line does not want cruises b/c it will change its times if it wants to. 

 

Thanks for any suggestions!

[budmeister]

That was supposed to say 1/ 2 day!