@gemlog Compose combinations are usually pretty intuitive, like Compose-1-2 gives you ½, Compose-^-e gives you ê, Compose-+-"-" is ± and so on. Unlike those obscure Windows Right Alt + 0151 for long dash or Alt + 0133 for ellipsis, although I remember some of those too 😆
Anyway, wtype would probably get your issues solved — it can type any character, just bind that to a key, with Sway it's easy, I'm not sure what you are using with Wayland but shouldn't be too hard with any WM.