Tea It's similar to yours, but it covers the whole of the inside of the cot, so imagine it will prevent her from smacking her head or at least I hope so. I got it from Amazon but am sure you can get it from other places too:
Baby Cot Bumper
bird and Bona H was like that just over a week ago so chances are they'll figure it out soon. She used to get really, really frustrated when her arm got on the way. She'd move her legs too, but not her head. She gets cross now though as can't always roll all the way back and it worries her. When she's lying down she keeps raising her head and shoulders a couple of inches for about 10 seconds then sighs and lets herself go back down again, it's so cute. She's 16 weeks though so she might just be going through a big growth stage :)
H is teething too and her teeth drive her nuts so it's a mix between bonjela and abensol or however you spell it. She chops on whatever she can get a hold of; teething ring, bottle, edge of a boy, boob anything bless her.
Her laughs are amazing too. I just melt when she laughs and she is a baby who does laugh a fair bit. She loves bouncy things and people shaking their heads back and forth :)