Jodi, PP's been a good student! :P Could you have the same problem as her? I found my BBH wool covers dipped in the front centre, just the way front closing cover seem to be shaped, and I don't find the larges to be that generous, I'd love to see a BBH XL size!!
Like PP said, some wool with a longer rise (pretty much any knitted cover) should do the job. If we're not using wool, we use Motherease Airflow side snapping PUL covers.

Maz that is freaking brilliant service! I hope BBH stuff something up for me one day!