I replaced mine with a Sleep Number RV King. Sleep Number makes RV versions that have radius corners if your RV needs this. When I bought mine Camping World was the only outlet for the RV King where the regular Sleep Number stores handled the Queen size.
I full time so the cost wasn't an issue for me and I absolutely detest mattress toppers, especially memory foam.
In researching what to buy at the time, I found a local mattress manufacturer that would make one for me even with the radius corners at the foot, but it weighed over 90 pounds. I was also looking at reducing the weight in the front of my 5'er, so the Sleep Number won out. I never regretted it and would buy a Sleep Number again. Another vote for the Sleep Number is you assemble it on site. Meaning you take the individual pieces into your bedroom and put them all together. Very easy vs trying to wrestle a king size mattress into a tight RV bedroom.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof