You can always have covers made for almost any chair. Maybe just look for 2 chairs that work with those

You could get a couple of chairs like these

Hooker Solana Wood Back Arm Chair Set of 2 · More Info

For making slipcover you will need to draw a template using the back of the chair add 1" for the seam , here is an idea for you :)

http://www.hgtv.com/design/make-and-celebrate/handmade/how-to-make-a-custom-dining-chair-slipcover

It would be a shame to slipcover these, as they are lovely chairs. I would purchase two captains chairs that compliment the shape of yours, but are different enough - it's a modern/interesting look. You could reupholster them all with the same fabric, or just redo the seats on your old chairs to compliment the new ones. You could even paint them all the same color if you felt you wanted to have more of a connection. If you do reupholster, there is a technique to getting neater corners and you could easily find on line, as I noticed the puckering...hope this helps - lol.

East Side Eden · More Info