Hey Reading_Bug.
Welcome to our Mattress Forum. 
What kinds of mattresses did you test? Pillow top? Hybrid? How did they feel?
Making sure to choose a product that uses good quality and durable materials will always be your best way to not have any potential issue with lasting durability.
To quote Phoenix
When you are heavier, I would tend to make sure that both the support layers and the comfort layers are firmer and higher quality than the “average” because firmer materials in both (and especially in the comfort layers) will tend to be more durable and suitable and will feel softer than they would for lighter weights. In some cases and with some types of mattress it may also be worth considering a thicker mattress and post #14 here has more about this. I would also consider a strong innerspring with good quality comfort layers as well as a latex/polyfoam hybrid if they are available in your area.
Wow! Have a retailer you can trust is half the equation. Do they manufacture any of their own beds, by chance?
NikkiTMU