I breastfed my dd for 13.5 months, but had only ever intended to get to 6 months!! I was more than ready to stop when she weaned herself, and in fact I probably had had enough after about 9 months if I'm honest.
I'd say if you want to breastfeed go in with an open mind. Ante-natal classes will sell it to you as if it is the easiest, most natural thing in the world, but for many women that's not the case. If you go in knowing that it might be difficult at first, but having an idea how to overcome those problems then you'll be less likely to think that you can't do it, and less likely to feel like a failure if you do encounter problems.
I didn't have an easy ride to start with, and I found the first six weeks the hardest ever. But I'm quite stubborn so was determined to crack it. In the first six weeks I had sore nipples, cracked nipples, mastitis, problems latching, oversupply, baby who took ages to feed and a low birthweight baby who I had to wake to feed every couple of hours at first. And I felt so alone, especially in the middle of the night, as I had no one who could answer all my problems.
Then after 6 weeks it started to get easier, and by 12 weeks I felt much more comfortable.
I had a book called "Breast is Best" by Dr Penny Stanway which had advice for all the problems I encountered, but dealt with it in a matter of fact and non-preachy way. So that really helped. Lansinoh cream was a godsend for sore and cracked nipples, expressing a little before a feed helped with the latching problems until my supply settled.
I will be breastfeeding this one too, and hoping I have an easier time of it. But I will be introducing a bottle at about 6 weeks too, as we are going to a wedding where children are not invited when baby will be about 6 months so my mum will have to look after baby all day then. And I am going back to work after 9 months this time and will wean baby off bf sooner this time.