I've started to do more work on my vast menagerie of bikes, as it's a welcome distraction after toiling in front of the screen all day; and destroying yet another old tee-shirt is getting a bit costly so time for some sort of overalls – are there any recommendations for work wear?
Standard boiler suit? More coverage. Think Guy Martin, not Kylie.
I like an old school workshop coat. Long sleeves and decent trouser coverage keeps everything clean. Probably more useful for metalwork and woodwork but does the job for fettling too. Easy on/off means I actually use it rather than thinking "this job won't be messy so I won't bother" (with obvious results)

I have both. The apron is probably better for fettling, you can take it off when you go in for tea and won't get harangued for sitting in the comfy chairs wearing your dirty troos.
Dungas better for all day outdoor jobs, processing firewood for example. Layering needs to be considered, you don't want to be wearing too many tops over them in case of an emergency poo. So best worn under the braces
A cheap onesie? Of course, accidents can happen…
A heavy-duty apron might be the most practical option.