I believe this worked for hunter-gatherers because they probably had their babies skin-to-skin almost 24/7. Today, it is said that "ecological" breastfeeding (using exclusively the breast for food, comfort, etc.-- no pacifiers, no bottles, and wearing your baby in a sling constantly, and co-sleeping), will result in suppressed fertility for at least one year. Americans tend to be more distal, using pacifiers, placing babies in bouncy seats, using bottles (even if it is breastmilk), etc. So it's not enough just to ask if breastfeeding in general will suppress fertility. You have to know what kind of breastfeeding you're doing.
I have a 12-week old and my cycle started coming back 6 weeks ago. I exclusively breastfeed, but I was using pumped bottles for several weeks, during which time my cycle returned (not sure if that is WHY my fertility wasn't suppressed, though). I also use pacifiers and although I use a sling often, I also use a stroller as well. I am quite certain that my fertility hasn't returned, however, because I use Natural Family Planning and know when I am having a fertile period each month. So far, my pre-pregnancy fertility signs have not returned, even though my cycle seems to be coming back (I say "seems" because I haven't had a regular, heavy period yet).
My advice to you would be to learn how to detect your own fertility. This is relatively simple. There are several methods. The great thing about this is that you do not need to use a barrier method or take hormonal contraceptives in order to naturally space out your children. While breastfeeding is a great way to suppress fertility, the only way to be sure that you are spacing your children is to abstain from sex during several days every month when you are ovulating (and it is very simple to learn when you are ovulating). Personally I observe cervical mucous and supplement with a fertility monitor, so I knew exactly what was happening pre-preg. Just Google "NFP"-- I like the Billings Method of NFP, but there are other excellent methods as well. And they are 98% effective. They can also be used to help achieve pregnancy for women who have tricky cycles or disorders such as PCOS.