Look for a fork that has mid-blade eyelets. Aside from the amount of eyelets, look for something that has a similar axle-to-crown length. Measure from the center of the hub to the bottom of the headset, I would expect the fork on this bike to be somewhere around 390-400mm. Grabbing a fork with a shorter axle-to-crown length will make the steering more twitchy and responsive, and will probably reduce tire clearance. Grabbing a fork with a longer axle-to-crown length will make the bike feel more stable and predictable when there isn't a lot of weight on the front end, but might have more of a tendency to flop to either side when there is a bunch of weight on the fork, and might give you more tire clearance. You probably don't want to go anymore than 10mm shorter or 20mm longer.
Before you grab a new fork, it is wise to decide on the rack you want to use up front. Some racks attach at the axle and would work fine with the stock fork, others will work best if you do swap to something with more eyelets. Or maybe take a look at the Crust Clydesdale fork.