I have Crohn's and had one very bad perianal fistula which eventually formed an abscess...and it was one of the most painful, horrendous things that I had to deal with since being diagnosed with Crohn's.
So, I am very sorry to hear you are having problems with abscesses.... :(
I did not have the surgery you said you are having, but I had something similar--when i had my ileostomy made, the surgeon removed my whole rectum and anus (basically, "carved out" my bum hole-), and sewed my bum shut. He said that this wound is very difficult to heal, and it takes a long time. From what I understand (though I am not a doctor, of course!!), the gracilis flap that your doctor mentioned is supposed to help this type of bum wound heal faster by replacing some of the "bum muscle" they are removing.
Even though they sewed me shut, my wound opened up a good bit later, so I have to put a bit of gauze up there to keep things dry and clean (the wound lets out a little bit of pinkish fluid, so the gauze catches this) until it heals more fully.
After my surgery, I was pretty much numb down there for 2 weeks or so, but after that, it was pretty sore and hurt to sit, so I laid on my side a lot. the good news is though, now that I don't have a rectumor anus, I can't get anymore periana abscesses!
I wish you luck in your surgery! Hang in there!!