+1 for the AC Guitars Mule.
I've managed to lay my hands on a couple of them, a fretted 5 and a fretless 4.
Both of them were marvellous, and the fretless 4 really had that Rob Allen, mini Double Bass thing going on.
Here's me noodling pointlessly on the fretted 5 >> https://www.instagram.com/p/Cj7-DXOA3NI/?utm_source=ig_web_copy_link
There are some lovely demos on the link already posted above too, https://acguitars.co.uk/mule/
Cheers,
Eude