If it's fully your home (not even mortgage), just go to Home Depot/Lowes for a replacement knob. I've changed all knobs on my home at least twice in the last decade-ish, it's super easy.
I recommend chrome/silver knobs for your home. If you have time, put that wire well around the frame, and paint it white. The bookcase is nice, and it just needs a refinish (even it it's vinyl). Everything else looks great, just dust the grates with a humid cloth.
