The Nordy mute is definitely the fastest on/off option but it is so expensive for a stick with some foam on it. And the foam is very hard and mutes massively.
A triangular shaped foam would allow the muting amount to be altered just but pushing it on more or easing it off - ideally with a softer foam...
That and the stupid price made me make my own ones. Plastic Ice Lolly stick. About £5 for 20 of them:
https://www.amazon.co.uk/dp/B06XY9JF3V?th=1
and then some adhesive backed foam tape:
https://www.amazon.co.uk/dp/B07VJXPD4B?th=1
(Just an example, you can get it a lot cheaper than that, for shorter amounts)
And you can make a bunch of them for various basses. Stick the foam to the lolly stick and then use a sharp knife to cut the slots to fit your instrument.
Can even shape the foam for more and less muting with just a pair of scissors. Cut the lolly stick down to size to remove the excess length.
I made enough for all my basses for about a quarter of the cost of a single Nordy one.