I suffer from Chronic abscesses and fistulas. Fistulas are evil. I currently have 3 including a recto-vag.
You don't say if you have crohn's or what kind of fistula surgery you will have.
Generally, you can't lift anything for 6 weeks but it depends on the type of surgery. You can purchase a "donut" to sit on after, especially during the car ride home. Keep the area exceptionally clean. Use a spray bottle after every bm to thoroughly clean. Frequent sitz baths will also help. Aside from that pain killers, good movies, pillows, treats and lots of TLC from loved ones will help
Good luck!