I'm a big fan of the 642, especially the no-lock version. I have one that is well-used; it's my primary carry gun. It does take some practice to become proficient with. Photoman44 gave some good tips for starting out with a 642, or any airweight J-frame.
For low recoil I've always liked the Federal 125gr Nyclad combined with any of the commonly available 130gr FMJ loads for a good carry/practice combination.
If possible, you might want to see if you and your wife can rent or borrow one to see if it'll work for either of you. While an airweight J-frame is an excellent self-defense gun, it isn't for everyone.
If you can afford it, it might be worth it to get a steel frame Centennial and a matching airweight Centennial. You can do the bulk of your practice with the steel gun, practicing occasionally with the airweight gun you carry. Or you may find that the steel frame gun by itself meets your needs.
And yes, the finish is the 642's weak spot. The finish on mine is particularly bad, but I've put about 800 rounds through it since I got it in January and perform dry-fire practice drills fairly regularly, so that may be a factor. There are people who have 642s with little to no wear, so it may be a bit of a coin toss as to whether or not you'd have finish issues.
Oh, and despite the finish problems I've had, I'd still get another one. The finish doesn't affect the gun's functioning, and I bought it to use as a tool, not a showpiece.