You might want to try the Matias Ergo Pro. I switched to it after 15 years on the MSFT Natural 4000. I still slightly prefer the 4000's layout and wrist rest, but the overall typing experience on the Matias is much better.
If you don't mind non-standard layouts, here are some excellent keyboards that give your thumbs more to do. :)
https://www.trulyergonomic.com/store/truly-ergonomic-mechani...