Some thoughts... I’m a Patreon patron, and can identify a few things I’ve seen. Often there may be Patreon only content (art, stories, videos, WIPs), that doesn’t show up elsewhere. Depending on the monthly tier level, I’ve seen small gifts to patrons (sketches, art), and patron specific raffles. Higher tiers I’ve seen free monthly art for a patron, or the artist is always available for commissions for the patron (seen at levels like $30-50/month). What you might offer really depends on the monthly tiers you’d provide.., and what time you have outside of commissions to do Patreon stuff. Some folks will simply want to support you... essentially a monthly tip... and not want anything in return. Others will be looking for something in return for higher tiers. With the amount I pay, I’m in the monthly tip category currently. I like that it’s automated and just bills me each month.

All the content you can offer while not stressing yourself out!
Maybe smaller doodles, wips, some mini-tips you have for others that draw aswell?
But honestly, anything you're willing to post on your Patreon people will appreciate 💙