I am looking into breeding my mare very soon...
She is a Quarter horse x ( the person I bought her off didn't know what she was crossed with
Anyway does it matter which breed of stallion I breed her with for best conformation with the foal?
Short answer: yes, it matters very much. Not just the breed but also the conformation of the stallion.
But the conformation of your mare matters as well. What are your plans for the foal? It would be very difficult to sell an unregistered foal.
I want to breed my mare as well, but only because she has exceptional conformation and amazing bloodlines, and it won't be for a long time yet. If I didn't think she was broodmare worthy, I wouldn't breed her. I'm not going to breed her just because she is a mare and can. I'm also waiting to see how she performs. If she performs poorly, conformation and lines are not enough of a reason for me to breed her. I need all three, AND an exceptional stallion.
Why do you want to breed your mare, and what are the plans for the baby? What traits make you want to breed your mare? How is her conformation? Her lines? Are there studs you are looking at?
I'm also not a bloodline snob, but I'm only going to breed an animal with good bloodlines because if A) I can't keep the baby for unforeseen reasons, I want to be able to find the baby the best possible home and B) I want to give the baby the best chance of success I can, starting with proven lines that produce good babies.
ETA: You also need plans for the baby's future. Do you want a western horse? English horse? Trail horse? That all changes the kind of studs you want to look at, and your mare needs to have the corresponding traits and conformation to match the stallion. If your mare has a long back, you want a stallion with a shorter back. But the most amazing stud in the world will NOT fix your mares conformational flaws. You need to have an amazing mare and good reasons to justify breeding her.