Mattress/bed upgrade?

We have an M-18 and have been sleeping on the orginal mattress with a memory foam pad and thick mattress pad but are looking to upgrade further. What have you guys done? Should we just buy a Queen size memory foam mattress or a spring mattress?

Our favorite is the Sealy pillow top with the 3 inch foam top built in. Bit pricey but is a great mattress.

we put a 3 inch memory foam on top of the original matress and it works well for us.