Haven't read all the other replies, but it's clear you've already gotten plenty of advice. I'd just like to add this:
Babies don't just suckle for milk. Please remember that they also nurse for comfort. If a baby is upset, sick or just longing for attention, it helps to let them suckle at the breast. This works for mine. When nothing else consoles my baby, I let him nurse. After a few minutes, he calms down or falls asleep.
I'm sorry you didn't enjoy breastfeeding. I'm doing it and am having problems (pain, swelling, supply problem, plus it's time-consuming to feed and pump). What I do is I breastfeed when I can, then use a pump to boost supply. If I'm busy or we want him to have a good night's sleep, we give formula. Just not too much. Formula keeps him full for a longer period, it gives you a break, and it lets Dad spend time feeding baby too.
I suggest you rent an electric Medela pump. I've tried it. It's fast and works very well. Also, once you get the hang of it, you'll be able to breastfeed while doing other things, like reading a book or using your laptop. I heard there are baby carriers or slings that make breastfeeding easier, but I've never tried it.
As for your tailbone problem. You should discuss it with your doctor. I set up a lot of pillows and blankets before BF to make sure both me and my baby are comfortable.
As for frequent feedings: Babies nurse often if it's BF because breast milk is easier to digest than formula. Also, it seems to be the natural way to eat until we are taught to have 3 big meals a day. It may be easier on your baby's digestive system. A newborn is just getting used to milk, so smaller feedings are gentler on him or her.
So my advice is, it's OK to supplement with formula. Just do try to breastfeed at least part of the time. Let your baby comfort-suckle. Get others in the family to help you so you won't be so stressed. Good luck to you and your new baby!