[carpdad]

If like above. If you are willing to cover that wall with plywood. You can cut doors in the panel. Measure, mark the line, cut the hinge side, screw on hinges, then cut 3 other sides. Finish the end cuts with handsaw. Should work with 1/2" plywood. Paint grade, sanded, luan. I would think multiple doors will make the access easier.

 

[imola ghost]

View attachment 717364
If like above. If you are willing to cover that wall with plywood. You can cut doors in the panel. Measure, mark the line, cut the hinge side, screw on hinges, then cut 3 other sides. Finish the end cuts with handsaw. Should work with 1/2" plywood. Paint grade, sanded, luan. I would think multiple doors will make the access easier.

Yes. Very similar.

But my room is fully finished with drywall, paint and baseboard.

 

[Jeekinz]

Fit a slab door with a latch and paint everything the wall color. You'll need to finish the cut edge of the sheetrock/framing since there is no trim. Add base to the bottom of the door too.

 

[carpdad]

I am suggesting that you remove the drywall and cover with plywood. More work but I think easy access is best for using up every space you find. Storage means you are using it and have reasonable access.
As such, another idea. Remove drywall, leave the studs although you will have to fish around them, frame the opening with clean 2x4, top/bottom frame, 2 sides and one middle. Then use bypass cabinet track with ball bearing frame for the doors.
Almost forgot, If that knee wall is just for divider and not load bearing frame, you can remove all studs.