Hi piperpilot,
A topper works in combination with the mattress underneath it so the most suitable choice for a topper will depend on the type of mattress it is used on (and how much thickness and softness it already has in the comfort layers). While only your own experience can know for certain if a mattress/topper combination provides you with good PPP (Posture and alignment, Pressure relief, and Personal preferences) there are some topper guidelines in post #2 here and the posts it links to (including some good sources) that may help you choose a topper based on your personal experience on the mattress you will be using under it as a guideline.
5 lb memory foam is good quality/density and Sleep Aid uses North American memory foam that is CertiPur certifed so it would meet the criteria I use for memory foam quality and they appear to have reasonable value as well although I would also compare them with some of the others on the list both in terms of cost and in terms of exchange or return policies in case you make a choice that isn’t ideal.
Phoenix