When my daughter got to be about six months old and started on baby food, she decreased the amount of milk she was using enough that my cycle started. I got pregnant right away and my girls are 15 months apart.
Trust me, 15 months apart is awesome now that they are 3 and 5. They are so close and entertain each other and love on each other (and fight, of course).
However, pregnant while taking care of a baby is really rough.. trying to deal with a crying newborn and a tantruming 16 month old is overwhelming... in fact the whole first year was a bit overwhelming for me. I'm not saying don't do it (I would do it all over again in a heartbeat), but be prepared and make sure you have a large support system in place... I'd advise waiting to get pregnant at least until your daughter is 6 months old..
Just another note, since breastfeeding is important to you, the pregnancy hormones change the flavor of the breastmilk just a tad.. Some babies keep on going like nothing happened. Others wean themselves. My older daughter weaned herself at 9 months and refused to take the breast - she actually preferred formula!!
Best of luck!! You are in for a real fun ride ;-)