The first thing I'd do on the bike is to remove the old fork, and measure the steer tube diameter at the crown race, as well as at the handlebar stem.

I'm wondering if that fork is "tapered", perhaps 1 1/8" at the stem, and 1 1/2" at the crown race.

If it was me, I'd probably try a headshock on that bike.

https://rstsuspension.com/en/forks/c...le-shock/ss-a7
https://rstsuspension.com/en/forks/c...ck/ss-m7-ss-m6



Now, I think the RST forks are only straight tube 1 1/8". If you have a tapered steer tube, you should be able to get away with an adapter for city use.