Well, you have fine taste!

I went 19 and 20.

I'm not sure you want to go narrower in the rear, wider is better. But I'm thinking you are trying to match the offset? Am I right? If so, use this tool:

http://www.rims-n-tires.com/rt_specs.jsp

Enter stock data on the left and new/proposed data on the right and fitment data appears below. If you do go wider in the rear, 35 mm offset might be all you can find.just add a 15 mm spacer and buy new lug bolts to match length. (You have to buy new ones anyhow. (Ball seat vs. Taper seat).

Figure out what you want for looks, and I'm sure me and other forum members will help you out with the rest.

Do a search on "spacers" and "fitment" and "tire sizes". to learn about some of this stuff. It's all been discussed before.