My DD was extremely restless and would kick and wriggle and grunt heaps. She never seemed unhappy about it.

Maybe she's just comfy on her side? I think that's ok Can you help her to sleep on her side in the cot? (using a wedge or something, maybe?) A rocker maybe isn't a great long-term option, as you say.
don't think they can lie on their sides in a hammock?

solids. well.... 2-3 feeds a night is pretty normal for a baby that age.