I am using the Contour Unimouse at work. Very customizable to your needs. I only find the choice for default button assignment a bit weird - it has 3 buttons + mouse wheel on top and the middle button has the same action assigned as the mouse wheel "button". Due to the size of the mouse and buttons I have the middle finger resting on the middle mouse button whereas on other mice the middle finger rests on the right mouse button. So you'll need to use their (not so great) software to change the button bindings. Other than that a very robust mouse with high customizability.

I used to be on the MX verticals too, but I have found a new love in the Protoarc EM11 NL vertical mouse. It is a higher quality product than it has any right to be for the price, and anyone here who likes vert mice I urge to try it. Still on my first but I bought another one for the office and another for a friend.

Not a vertical mouse:

I have a Ploopy mouse (specifically the thumb). It has different enough way of using it that I haven't suffered wrist strain since.

Everything is open source and all physical parts are 3D printed. I've replaced 1 broken part twice so far.

A trackball mouse does take some time getting used to, and never quite achieves the accuracy of a regular mouse.

This is the Canadian link but I'm using the Keychron M5 ... feels solid for now, I hope it stays that way. It's very light and it's kinda meant for gaming.

https://keychron.ca/products/keychron-m5-wireless-ergonomic-mouse

I've spent a small fortune on trackballs, keyboards and mice ...

Not quite the same, but if there's hard plastic under the coating you could strip it down with solvent and replace it with a different material. Pleather would be comfortable and durable.

I originally tried a Kensington Pro Fit Ergo, but it didn't last very long. When I went looking again, the MX Ergo had come out. You can adjust it between a more flat or vertical configuration, and it has worked great for me for years now (although since there is a trackball, you do have to pop it out and clean it on occasion). I have had issues with the MX Masters before I switched to vertical mice, so it doesn't surprise me to hear that you were having issues with MX previously. It sounds like you aren't looking specifically for vertical mice with a thumb trackball, but I would seriously consider making the switch since you're using them for ergonomic reasons. It doesn't take long to adjust to it, and it essentially completely removes the wrist movements you would make with a standard vertical mouse. However, last I looked, there were very few options for that configuration. If you opt to go with a vertical trackball, I would also recommend a cushioned mouse pad for additional wrist support (plus a wrist guard for the keyboard, and compression gloves if you're dealing with any wrist pain).

I wish you luck with your search!

Honestly, the 3M Wireless Ergonomic Mouse is my favorite ergonomic mouse. It's also quite durable. I used it at work for years as my main driver when I had wrist pain.