There are a ton of thin matresses on amazon Like this one https://www.amazon.com/dp/B00PWM8YD6/ref=cm_sw_r_cp_apa_fabc_idrWFb3S8P82F?_encoding=UTF8&psc=1 Or anything similar. . I'd suggest doing something like this. A thin, foam/memory foam mattress you can cut to whatever shape/size you want. It's also beneficial because you can roll it up and secure it for when you're not using it. Or get a few layers of matress topper/memory foam/egg shell type things and those can also be cut to exactly what you need. I'm doing a Mazda Cx7 and it's very roomy but awkwardly shaped on the inside.
Another sleeping option is small memory foam mattress. I recently bought this on Amazon. It's a bit more expensive, and a bit harder to store (you can roll it up a bit, but it does take up space). Got fed up with air mattresses developing holes.
Hi there. I work for GoodMorning.com and just wanted to chime in.
As a side sleeper at 210 lbs, a medium firmness would probably be a better fit for you (if you get a mattress that is too soft, you risk sinking in too deep and having improper spinal alignment). If you are looking for an inexpensive option, here are a few medium mattresses that might be a good fit:
We hope this is helpful! Happy shopping!
Classic Brands Cool Gel Memory Foam 6-Inch Mattress, CertiPUR-US Certified, Twin https://www.amazon.com/dp/B00PWM8YD6/ref=cm_sw_r_cp_api_i_B9n8Db9KEV48E