First of all, I'm so sorry about your loss. I'm sure it's been a difficult process for you and your hubby.
I've been giving this a LOT of thought lately myself. Don't get me wrong, I would LOVE to just keep my current boys forever and not have to worry about getting another someday, but I know the day will come when I will be in your shoes looking for another dog to add to my family. I don't need material things in my life... I need animals... My oldest boy who will be 9 in March was just diagnosed with ARVC. My other boy has been in great health, but after Riley's scare I really learned how precious every day really is with them.
I'm torn for the same exact reasons you and your hubby are torn. I want so badly to rescue and give a homeless dog a good home, but at the same time there are so many unknowns. We probably won't know of their history / bloodlines so we wouldn't know if they're more likely to get cancer or heart related problems. Also, we won't know how they are with small kids and/or other pets (in some cases). Whereas with a puppy you would have all of these answers.
I guess you just have to weigh the pros and cons of both. Would giving a homeless animal in need a second chance of having a happy and loving forever home outweigh the money you could potentially end up paying should complications arise?
On the flip side, you could always spend a lot of money up front for a quality puppy from a breeder where you know the history and bloodlines and then end up having to pay to fix a broken leg or a torn ACL, etc. There's also still NO guarantee that this said puppy couldn't still end up getting cancer or developing heart problems much like a human who gets cancer when there's no history in the family.
It's just such a difficult thing to decide on. There's no right or wrong, it's about what feels right to you. I guess you and your hubby will just need to sit down together and really talk this out. Who knows, maybe you could meet in the middle. Adopt a younger boxer now and then add a puppy to the mix a little later or vice versa. Good luck with your decision.