I too would like a fatter wheel, arthritic fingers struggle on thin wheels.
I am still unsure about the best way to do it. ...
I can identify with arthritic fingers prefering a thicker steering wheel.
There was a thread some time ago (thus on the old forum) from which I picked up a recommendation for a suitable thick steering wheel cover.
I bought one in October 2017 for about £15.00, but so far have failed to fit it 100%. This cover 'stretched' over the rim, there was no need for stitching.
I have got it on far enough to be able to say the standard rim is 18-20mm in diameter, while the covered rim is 30-35mm in diameter. The variance is whether you are measuring front to back or from the outside to the inside of the rim.
It was a 'Cosmos ORBIT TRUCK Universal Leatherlook Large Steering Wheel Cover (41-43cm)'.
I have just searched on eBay and the supplier I used is no longer active. I also searched '41-43cm' and while this brings up various wheel cover adverts, they all offer the 'alca' wheel cover, which in appearance does not match mine. The same applies to search results via Google.
While I started with the best of intentions I'm afraid this mainly tells you is that the size you want is '41-43cm', and an indication as to the increase in rim diameter that can be achieved with just a single cover.
In my opinion, if you want to bulk the rim out first you are best with a lace on cover, but these do vary, in my experience on other vehicles the cheaper ones can move around the rim (not around the wheel).
Regards.