Depending on how heavy and vigorous you and your partner(s) are you may be best getting a medium to firm pocketsprung one. Nothing worse than bottoming out the springs when kneeling or standing on the bed.
If you can't sleep on a firm mattress then perhaps get a thicker memory foam topper that's removable.
When you check the mattresses for compression under your weight be sure to sit around the edges, again no fun if they collapse during various positions.
I've never been very impressed by the Ikea lot. If you're splashing out on a good quality one in the region of 2 grand or more then look at the John Lewis own brand offerings too.
Tested the Emma and Simba recently at Dreams and for all the hype wasn't that impressed with the former whilst the latter had some good offerings but at their price point I thought there were better value with other brands, whether cheaper with same feel or better for similar price.
If you try to get a sneaky bounce test in when the salespersons aren't looking, just check for CCTV unless you're fine with going viral.
