Sleeping pad or air mattress?
Instead of uncomfortable sleeping pads, I recommend inflatable mats made of Rip Stop fabric. There are three sensible options available at present: Big Agnes Air Core model, weighing around 700g - USD 55; Air Core Clearview model (made of polyurethane film), weighing around 480g - USD 90; and Term-a-Rest Neoair weighing 410g - USD 150. The last one is available at Decathlon for PLN 539. Sleeping on such a mattress is extremely comfortable, its thermal comfort surpassing that of sleeping pads by far, because of the 5cm thick air-filled layer.

You can find it in camping stores. An alternative solution might be a self-inflating mattress, but in my opinion, being thinner (2-3 cm) and relatively heavy, it is not as good as the above-mentioned mat.