Do you put some kind of framework in the bag as has been mentioned?
Ilford's Pop-Up Darkroom is impressive with a price tag to match. Probably overkill for my needs at the moment.
I hadn't thought of putting foil over the window, but that would be expedient and inexpensive.
I haven't tried any framework in my dark bag, so occasionally the material gets in the way but it's not a problem inasmuch as I can solve it in under a second.
When I do proper printing, I actually have to use the spare bedroom in my mother's house due to lack of space at mine. So I darken it by taping foil to the windows and working at night, usually in November/December when it gets dark really early here to give me six clear hours before I start feeling like it's time for bed.
Moving forward to when I have a bigger place, I intend to either have a room which can be converted into a darkroom or buy Ilford's pop up dark tent. It's not expensive for what it is, no more than a regular camping tent which doesn't keep out the light. Though in recent years there have been a small number of tents advertising "blackout bedroom pods" which may be where some bright spark at Ilford/Harman got the idea.