Last spring, I had an REI city commuter converted to an eBike. The specific model converted is a 2015 Novara Gotham. The motor I had installed is a mid-drive 500w Bafang 8fun. The bike is pretty fast…20 mph with average pedaling at level 3 (of 5) pedal assist. And I can do 30 mph on the flat if I pedal hard. Anyway, I quickly discovered that the bike path between my Arlington, VA home and the downtown DC location where I work was beating the heck out of my spine. The bike I converted has no suspension (a clear mistake). So I purchased a Tamer Pivot Plus XC Suspension Seatpost.
http://www.niagaracycle.com/categor...YobNxptHrQcobRYqwuqdsG23wRjmI7Jj9MBoCXf7w_wcB. It appears similar to a Thudbuster, but at lower cost.
I coupled that with a Bell Memory Foam Saddle
https://www.amazon.com/gp/product/B001D16OCI/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
Yes, I know…this seat is not a top of the line product like your Brooks saddle, but I’m an old guy and this combination made all the difference for my 10-mile commute. I ride to work effortlessly. My back and butt do not hurt when I get there or home. And I get some exercise, especially on the way home since it’s mostly uphill.
I've ridden this bike 40+ miles at a stretch along the bumpy C&O Canal tow path with that seat and seat post treating me almost as well as a full suspension bike. That said, I know there are higher end components that would perhaps serve you better, but this setup has worked out well for me.
Good luck to you in finding the configuration that works for you.