How necessary is it to be a total surprise?
One thing that DH and I have occasionally done that is wonderful:
1. I make a Wishlist of Kindle books that I want and he buys some of them for me.
2. One year we each looked on Amazon and found some things that we wanted but maybe wouldn't have bought for ourselves and then sent the links to the other who would buy one of the item.
3. I just bought some things from the LL Bean catalog. They really had a lot of nice stuff. Have her go through the catalog for there (or somewhere else) and circle the items she thinks she would like
4. A gift certificate to some place she likes but you want her to pick out what she gets. Last year I requested DH give me a gift certificate to Pandora because I wanted to make a bracelet. Since then I've marked a wishlist of charms that I would like to receive as gifts. So DH can just look at those.
5. Look at things that she has and loves, but might want an update. An example from DH's birthday this year. He had a ChargeHR Fitbit. He liked it, but there was a newer model the ChargeHR 2 that had just come out. It has features that I knew he would like, but I also knew he was reluctant to just replace his ChargeHR since it was still functional. But, I knew he really liked the new features. So I solved his dilemma by buying him the ChargeHR 2. So, for your wife, maybe look to see what she has that she might be happy to upgrade or get in a newer form but might not leap to do it herself.