Is a modifier+space not convenient?

Which modifier+space produces U+202F? Alt+Space produce No-Break Space (NBSP) U+00A0 which is different and lacks the appropriate narrowness.

EDIT: I tried alt+space, alt-shift+space, alt-ctrl+space, alt-shift-control+space, shift+space. All produce either U+00A0 or U+0020 and other combinations, such as including Cmd doesn't work at all.

Sorry, I meant adjusting your layout with Ukelele or using a keyboard remapping tool like Karabiner Elements, where you can bind any modifier + space to insert any space (and KE can include Cmd and differentiate between left and right sides). You could even have a Ctrl+Space deadkey for less frequently used spaces, where any subsequent letter will print a mnemonic space (m-em space, f-figure space, b-no-break etc).

(And with KE even have a delayed notification to remind you which letter means which space if you don't complete this deadkey within, say, a second)

Thanks, good suggestion -- I usually try to avoid extensions as much as possible for many reasons (incl. that Apple actually discourages it), but I'll look into it.

Where does Apple discourages using your own keyboard layout (not KE)?

Though I personally would be easily discouraged if they made good native keybinding support

I wrote extension, not layout. I succeed finally with Ukelele thanks.