One thing that might help allay your fears if you haven't actually seen cardiologist (not vet) heart clearances/ MRI scans from the breeder is to ask them about the longevity of their lines. At least if they can tell you that parents, grandparents, great grandparents are either making it to 5 plus without a murmur or surviving to 12 plus .... basically, they're doing well.
I don't have official clearances either, which I now regret, but I did research my younger dog's pedigree thoroughly and there's a high number of recent ancestors on the heart clearance list AND her paternal grandparents at least lived well past ten years.
But do, do get the best insurance you can, and make sure it does offer cover for hereditary conditions. If you're in the UK M&S is pretty good, although the seem to have put their premiums up lately. Basically, DON'T stop reading about SM/MVD - you do need to know something about both. Most of us will have to face MVD at some point. On the other hand, don't borrow trouble either. You know that they say : hope for the best and prepare for the worst. Don't let it spoil your pleasure in your new baby. I've had my girls for five and two years and in all that time the only non-vaccination thing I've had either to the vet for is for a tummy bug when Holly was a pup, but I feel better in myself knowing that I'm informed.
Holly - 7years
Amber- 3 years