Hi T2000,
Try this page as a starter as it's the CAA reference for respiratory issues.
CAA Respitory Protocols
I had a major battle with them in the eighties about flying with a Ventolin inhaler and became the first pilot ever to be certified to fly with one single crew. That said, I'm not aware of any current peak flow limits as it's not a test routinely done unless evidence of breathing issues exists. Everyone is different so a figure of 550 for you might not suit someone else.
It sounds like you're making the right plans and doing the right thing so keep at it, but rest assured that there are many airline pilots whose waist lines now exceed their years in aviation both in inches, and in some cases centimetres!