Sorry to say but you seem to have completed the first step into even more aches on your rides. Hand numbness comes from nerves of the spine compressed by the body weight while riding in the upright position. The next step is to replace your seat with a "wide, soft, comfortable" one leading to even more aches.
You could be far better off Paul by keeping your flat handlebars and installing SQlab Innerbarends...
I was actually having numbness in my right hand before I switched out the handlebars. And I’m not totally upright, even with the swept back handlebars. My hunch is that my wrists are bent and that’s compressing the ulnar or the medial nerve.
These were the things that worked out for me, after trying multiple grips and setups. Like these grips for the multiple grip positions for long rides, and the adjustable stem allows trying different angles and heights.