My gut reaction is to a low-key adolescent female, a little on the submissive side. If you're up to it and want to earn some angel wings, you might even consider a shy female who would benefit from your male's good socialization, and draw confidence from him. I've seen several females like that bond very deeply with slightly older, well socialized males--it's neat when the males become very nurturing of them.
I love the foster-to-adopt idea!
If that's not an option, be very clear with the rescue that you need a play date (or two) at a dog park during hours when the park is pretty empty (early AM, usually). Also, you want a lengthy home visit with the dog. My home visits are usually a couple of hours long for this very reason. Some rescues will also let you try a dog out over a weekend.
Also, mind the introduction of the dogs at home to maximize your chance of success. I strongly recommend that you meet the dog you are considering in your front yard, with your dog already leashed up, and then you all go for a walk as a pack through the neighborhood instead of doing a dog-to-dog greeting right away. The dogs sniff each other as they are walking and moving, but it takes the tension way down. After a nice walk, then everyone goes into the backyard together, and if things are going well, leashes get dropped, so the dogs can interact now. After a while, everyone goes in the house together. This method works SO much better than just walking into the house with a a new dog.
Tell us more about your male, and we can offer more thoughts about what kind of dog to look for. What dogs does he react to? What dogs does he play with?