insole shoe problem

1. Problem with fitting an insole to a sandal

I’m trying to modify a sandal by adding an insole generated from a plantoscope. The problem is that when I bring the insole into Blender and try to attach it to the sandal, I don’t know how to properly adjust or modify the insole so that it fits completely flush with the sandal. 

2. Problem extruding faces without affecting the insole

Once I have the insole positioned inside the Croc, I can’t manage to extrude only the necessary faces of the sandal mesh to match the insole. Whenever I try, the extrusion ends up “eating into” the insole or deleting part of it. 

Any tips, workflows, or modifiers that could help me solve these issues would be greatly appreciated. Thanks in advance!