When I bought my Z710A ZTR, there wasn't any Suspension Seat available that would fit. The "higher cost" Z915B...big brother to the Z710A has one as an option, but, it will not bolt up on the Z710A.... Don't know the reason, and probably never will get an answer.
I was at Sear about three years ago and as looking at their lawn tractors and notice the way they had a suspension style of seat. Spring loaded as you may call it. I searched on ebay and found a used set of Craftsman Seat Spring #124181X for about $12.00 and free shipping.
I ordered than and when they arrived and painted the springs the famous JD green and left the plastic/rubber caps black. Here is how I have my "not too expensive" suspension seat. BTW: It works very well.