I did switch, but I hadn't been feeding him anywhere near as long as you, so not sure how much help this will be!
We switched from breast to formula at 4 days. I was just in too much pain from the delivery to deal with the bleeding and constantly throbbing nipples on top. Simply sitting down was a very painful procedure, let alone trying to manouvre a wriggling baby into position. We really struggled with latching on, and I was dreading every feed. My family encouraged me to give up when they saw me drenching him with tears.
So, we switched to formula and haven't looked back. He took to it instantly, and there was none of the messing around that we'd had with breastfeeding - the bottle went in and away we went. Dylan seems the type of baby that is very adaptable to change, and he just took it in his stride - in fact I think he was happier for it.
We had to experiment a bit to get the right temperature for him - room temperature made him very sicky indeed (still some stains to get out of the carpet). When he was breastfed, he didn't bring a drop back or get any wind. Since we sorted out the temperature of the formula, he usually only brought back a small dribble, but because he got a lot more wind, occasionally he brings a larger amount back if the milk got in the way of the burp. He does burps that would compare favourably with friday night in Weatherspoons now!
I do have some regrets about not feeding him myself, as I had always planned to. It's hard not to feel guilty when there is so much pressure on you, regardless of your reasons. I wonder if it would have got better if I had stuck it out, but knowing the pain I was in for the first 6 weeks anyway, I think I would have had to admit defeat sooner or later. I just wish things could have been different.
What you need to be prepared for if you decide to switch is the 'breastfeeding police'. Honestly, sometimes I am made to feel like a criminal, or at least a complete failure by the things people say, or by the look they give you when you tell them. I'm sorry to say that this applies to professonals and other mums. Unfortunately you can't make offical complaints about the way someone looked at you, but it still hurts.
All in all, I know I did the right thing for my family, and my son is thriving on it. Do what's right for your family, but be prepared to stand up for yourself.