This may be a strange question.
Background: I usually work in a multiple monitor setup, where I can plaster the screen with all my windows so nothing I might need to switch to is ever hidden from view.
On a laptop, that's obviously not possible.
A while ago I wrote scripts that give me keyboard shortcuts to move windows around into half/quarter/other convenient arrangements for essentially gridding the display. In researching this question I learned that these are essentially duplicated by some open source apps, but I found nothing that solves the greater problem of switching between these windows easily and painlessly.
In particular, I use spaces as a substitute for multiple monitors, plastering each one with a grid of windows. But I often find myself frustratedly trying to switch between applications in different spaces with no quick way to do it.
E.g. cmd-tabbing to the application makes me go linearly through a bunch of open applications and doesn't pick up applications open only in other spaces.
Using mission control only shows me the windows open in the present space; I have to switch spaces first to use it to get at another window open in another space.
I've considered using only one space and switching via mission control, but having only one space can lead to serious window clutter, with windows hiding behind each other and ending up in the "wrong order" so when I need to drag things between windows, etc., they're not activated at the right time. (In separate spaces I can leave paired windows side by side with nothing in front of them.)
I'm wondering whether someone else who has faced these frustrations has come up with a clever solution or workflow. I'd prefer something open source but am willing to learn a new workflow even with a steep learning curve if it means faster performance eventually--where performance is defined, I think, as reliably and quickly switching between many open windows, though I may end up editing this question as answers reveal that I'm actually looking for something more detailed. E.g. if a multiple-window-using guru of window-management best-practices can explain something like "I faced this problem, and I realized after many years that the right way to do it is work in a single monitor, and always follow steps A B C, and use tool D" then I am all ears.