The Cybertruck is the hardest Tesla to fit: it is a truck with a separate cab and bed, and none of the 19 mattresses compared is cut for it. Here is what that leaves.
None of the 19 mattresses compared is cut for the Cybertruck. The Tesery Air Mattress ($119) is sold as one version for the Model 3, Y, S and X, and Tesery's Cybertruck mattress is a separate $79 foam product that is not scored here. EXPED MegaMat Auto and HEST Dually are general pads, not cut for the Cybertruck, so measure your cab or bed before you buy. The HEST is sized for truck beds, but it is sold in the US only.
Tesery sells a separate $79 foam mattress for the Cybertruck. It is not one of the 19 compared, so it has no score here. The Tesery review linked above covers the Air Mattress ($119, #16 of 19), which has no Cybertruck version.
Two layers of foam, 10 cm thick, no pump. Sized for truck beds in general, not cut for the Cybertruck: sizes run from 163 to 198 cm long and 127 to 152 cm wide, so check them against your bed. Sold in the US only.
Self-inflating foam with an R-value of 8.1. A general pad of 197 × 132 cm (104 cm at the foot), not cut for the Cybertruck, so measure first. Out of stock at EXPED USA and REI on 1 Oct.