wayfair is the best one i have bought .
https://www.wayfair.com/bed-bath/pdp...002329503.html
a queen is Mattress Overall 60'' W x 80'' L. Trim off the extra with a Electric carving knife.
if you like a firm bed i bought this one too. no trimming necessary its a short rv one
LUCID 10 Inch 2019 Gel Memory Foam Mattress - Medium Firm Feel - CertiPUR-US Certified (Short Queen)
https://www.amazon.com/dp/B0088YUYF6...ing=UTF8&psc=1
i also got 2 of these and put them on hte bunks. the bunks where rounded corners so i used a electric knife and trimmed them then just sowed the cover back to match with a lick and a promise its going to have sheets one it anyways.
Zinus 6 Inch Green Tea Memory Foam Mattress / CertiPUR-US Certified / Bed-in-a-Box / Pressure Relieving, Full
by Amazon.com
https://www.amazon.com/dp/B01MT85NGJ...ing=UTF8&psc=1