Hi spkimball,
The Ultimate Dreams Eurotop is also a latex/polyfoam hybrid and does have some very general similarities to the Pranasleep Asana although it has much better value and has an exchangeable comfort layer so it can be customized to your preference both before and after a purchase while the Asana is a finished mattress that can’t be changed or made softer or firmer after your purchase.
A box spring (the kind that flexes and has springs) isn’t necessary or even desirable in many cases with a latex or other type of foam mattress but you will need either a foundation or a firm even support system (such as a platform bed) that provides good even support for the mattress.
The foundation thread here includes more information and links to many good options.
This would put you in a catch 22 situation because if you are dealing with a good manufacturer or retailer with good experience and knowledge (which are the only ones I would normally deal with) … they are by far the best source of the very information you would need to make a good decision. They would know more about their mattresses than anyone else and talking to them is one of the first things I would do and in most cases you will find them to be an essential part of the process.
Phoenix