Based on your 17x22 paper and assuming the image is maybe 1/2" in from the edge, a frame of 22x28 would work. That is a standard size you should be able to get.
You would then get 2 mats out of a 32x40 sheet of mat board.
One thing I agree with is to not lock your images into a standard size. Let your image tell you what it needs. You might want to crop the bottom third of the image to get a bit more drama and now it doesn't fit any "standard" size.
Find those frame companies who sell you frame sizes by the inch and get what the image needs.
When you present your work in a more professional manner, the customer will think that you ARE more professional than the next guy who has crammed his images into a frame that he uses because he can buy them by the box for almost nothing.
If the customer sees you in that way, he is more likely to go ahead and drop money for it. If he sees your image in a frame that isn't the right proportion, he knows he will have to redo the piece before he hangs it in his home... which means he will have to shell out even MORE money, making him pause and possibly walk on by without buying.
Scrimping on presentation leads to fewer sales.
As much as i think you should have a professional framer do ALL of your work
.. you can create a professional look with a bit more thought and planning than just "what's the next standard size frame to fit the paper".