Have you considered something like the NeoAir (admittedly not as warm as Prolite 4), or a custom DAM from someone like Kookabay?
I'm a back sleeper, so I can't comment specifically RE: side sleeping, but the TorsoLite didn't spin my wheels, especially considering it weighs as much as a NeoAir short. I actually preferred a RidgeRest cut down to torso sized compared to the torsoLite, but sleeping mats are a pretty individual thing. For instance I was never really comfy on a 4 inch thick Stephenson's DAM. It was too high off the ground and made me a bit sea-sick! Go figure.