Have a look at a push release for a loft hatch, this would work as you require but it would not sit flush with the flap.

How about a counterweight and rope, which would make it much easier to open?

@Seabornman I'd thought about it, but wasn't sure how to set it up to stay up without knots -I know how how to tie them, but my partner's skills in that area are impossibly bad•

@MBH Carpentry and Joinery Ltd. Push release feels risky, like: it'll fall down if someone leans on it going up or down the stairs?

@greg_2015 gas Struts! I can only find cabinet/lightweight ones.. Don't know where to look for sturdier ones. Ideas? ( I'm in Canada )

like so:

The one I was talking about has a hook connection so when if it was being used as a normal loft hatch when you close the I’d up into the ceiling the hook engages into a socket to ensure it stays closed. Then you push it up to release it to drop the hatch down. In your instance it would be fixed so that when you open the hatch it would stay open as the hook engages and would then need a push do disengage before closing. Hope that makes sense.