I couldn't breastfeed either and this is what we did:
Formula:
First of all baby was drinking around 1 ounce at a time every three hours, the first two weeks she was not even finishing that)
We just upped the amount to 2oz when she finished 1 oz easily, then upped that to 3oz etc There is a guideline on amounts at the back of the cartons of formula.
First we bought aptimil as well as that was what the hospital were using, then we bought Hipp Organic.
bottles: We bought tommee tippee bottles, they came with number 1 teats which is suitable for newborns, I think they were bpa free too.
Sterilising: We also got a tommee tippee steam steriliser, really easy to use, just plug it in, put the bottles in and 5 minutes later its done.
I used to take the bottles out and put them upside down on a wire rack so they'd dry out, sometimes I would rinse them with freshly boiled water so that there wouldn't be any drops and it would dry out completely, then I could close them and take them out and there wouldn't be any steam left at all.
Making up the bottles:
I used to boil some water in the evening and put it into flasks so I could use it the next day, it would then be the right temperature.
You shouldn't use mineral water unless you have to because of the mineral content. In some countries like Cyprus they sell baby water at the chemist, it's basically mineral water with a low mineral content. (rip off basically.)
We also pre-measured the formula in tommee tippee powder dispensers
Then when baby needed milk it was usually the right temperature and it was quick to do.
Formula will mix better with hot/warm water rather than cold (it can block the teat if it's not mixed properly.)
Try to change the teat when the baby is taking more than half an hour to drink his bottle.
The guilt is awful because that is pretty much the first question other mums ask you when you meet up at toddlers groups etc and mothers who breastfeed need support because it is hard so they talk about it and you feel like they're looking down on you when they probably aren't.
It gets better when at least some of your mates stop breastfeeding around 6 months.
After that what way the babies were fed is irrelevant.
hope this helps!