Hi Mysterium,
I’m sorry to hear that returning your Best Price Mattress isn’t a viable option for you, and that it’s not working out as is.
Your idea about using a topper certainly is a viable alternative that many people find comfortable. Speaking personally, I find a layer of latex on top of memory foam to be quite comfortable, but that again is my own personal opinion.
If you do decide to move forward with a 3" latex topper as you described, I’d be very interested in hearing how that works out for you.
Some of the better sources for toppers of which I am aware are listed in post #4 here.
Good luck!
Phoenix