Sasha - you may find you get better answers to your questions if you put your location in your profile, so that it appears on the left.
regarding your comfrey question - comfrey is usually propagated by
root cuttings rather than seeds. Fertile comfrey, grown from seed, has more potential to be invasive and spread where you don't want it. The sterile "Bocking" varieties are more well behaved in the landscape and you can easily divide a mature plant and make 20+ root cuttings.
Here is the UK ebay page with root cuttings for sale:
Comfrey root cuttings
I bought 6 root cuttings a few years ago. All of them survived transplanting, and all of them have since been divided at least once. I now have comfrey along fencelines, around fruit
trees, adjacent to
compost heaps etc...