Hi Padillam5.
Congratulations on your new Flexus hybrid!
With regards to a breathable mattress cover, you may be interested in this forum topic and comprehensive reply by Phoenix.
And touching on quality, breathable bedding… bedding made from natural fibers or viscose materials (like bamboo) will also tend to be cooler than synthetic fibers and linen sheets along with silk are probably the coolest of all the natural fibers for those where the sleeping temperature is a main priority.
Since bedding is not our expertise, I am unable to point you in the direction of any particular brand, but I do hope this helps!
NikkiTMU