I'm trying to extrude an area inwards, so that the new boundary is a constant distance from the old boundary. Essentially, the piece now has exactly the same size and shape as the hole that I have, but I want there to be a constant gap between my piece and the hole.
I've looked at this answer, but it doesn't give me what I want.
Here is the original object:
This is a sketch of what I want:
Here's what I have tried:
Extrude region (vertex normals):
How can I get what I want?
EDIT: Here is what happens if I use the solidify modifier:
It sort of works, but the distance between the new wall and the old one isn't uniform. This is how it looks like (the distances highlighted in red should be uniform, but they aren't):