Hi, I was in the same situation a few years ago and decided to take Maths as a degree first, just incase I didn't get on with Primary teaching.
The first thing I'd advise is that if you do take a degree first, you need to be really into whatever subject you decide to take. You have to work non-stop on this one subject for 3 years and it's going to be pretty boring and difficult if you don't really have a passion for the subject.
Secondly, in all of the PGCE interviews you are asked to explain the relevance of your subject to Primary teaching, so you need to make sure it's not a degree like media studies. Obviously English, Maths, Science are some really good degrees to pick as they are core subjects.
You could take a BEd, I don't think there's much difference in pay when you go into the field, as I imagine it all depends on how well you teach in the classroom. If you are going to hate 3 years of your life taking a degree not really related to what you want to do, then you should take a BEd.
It also depends if you're 100% certain that you want to be a Primary School Teacher. If you get a degree first you can get another high paying job later on in life, or teach secondary. If you get a BEd, you're basically stuck in Primary Teaching forever.
Hope this helps