You may want to go one step past normal spats and gaiters and actually create a shoe cover, or just make sure your spat pattern covers more of your shoe than a typical pair of spats. It will probably be easiest to go about making the pattern using the duct tape method. Put on your shoes and braces so you are sizing your pattern to go over them. Then take some scrap fabric, wrap it around your shoe and braces, and tape it so the duct tape is a mold of your foot, ankle, and calf. Draw the locations of the seams (front, back, and outer side) with a marker. If it will help create a smoothly fitting pattern which is more likely to stay close to your shoes, you can add other seam locations, like a toe piece. Carefully cut off the duct tape mold following one of those lines. Label the pieces, cut them, and then copy them onto flat paper as closely as possible. There are a lot of YouTube videos describing how to create patterns from duct tape, so check there for some visual aids if you’re not clear on the process. I’ll also be happy to try and help if you run into specific problems while making your spats. You should be able to decorate them however you please, or leave them plain. I would just recommend a removable keeper strap for under the shoe, to help them stay in place irregardless of your movements. Removable is important because flat shoes will wear out the keeper, so you’ll want to be able to easily replace it.