Mattress topper - what thickness

I use a 3 inch on my cabover bed. It helps tremendously. A 4 inch would have taken too much of the already limited vertical space. I have a 2 inch for my occasional use jackknife sofa. Even it is bulkier than expected especially once rolled out for the first time-and rolled back up. It is bulky enough that I leave it at home unless I anticipate needing the bed.

Just check weights and rolled sizes and get the thickest (heaviest) you think you can deal with.