Man just looking at all that cool water wants to make me a dip :-)
I actually searched the first few options you mentioned and especially liked the Yellow Spa and Prirodni Koupaliste Motol. The area not only looks like a place to cool yourself down on a hot summer day (like this one!) but it is beautiful and picturesque too.
Yep, you just have to find something to cool down those days.... For some people from other parts of the world those temperatures are nothing much really but for here it is getting little extreme....