I know that some people disagree with this decision, but we do not accept "laying" even if some native speakers use it. Just like we do not accept things that can be said by Polish native speakers but are considered grammatically wrong.
Never and... never ;)
It's Locative here, it simply denotes location (on the bed). (not literally all prepositions denoting location take Locative, but most of them).
The alternative is Accusative, mostly used with movement.
Skaczę na łóżku = I am jumping on the bed = Locative.
Skaczę na łóżko = I am jumping... to? the bed (from the floor on the bed) = Accusative.