You're right, there are a lot of choices out there! Booster seats are not safe until a child is at least 4 years old and weighs at least 40 pounds (manufacturers will say 3 years and 30 pounds, but I have several friends who are carseat technicians and they all disagree with the carseat manufacturers--a big part of the reason they disagree is because a child is not developmentally ready to handle the "freedom" a booster seat offers until at least age 4. A 5-point harness is still safer than a booster seat, even at age 4, but there aren't many available that are safe for a child heavier than 40 pounds (there are a few, Britax in particular makes some seats with 5-point harnesses that go up to 65 or 80 pounds--they're just very large and very expensive and for some families that makes them a bad choice). At 13 months, if your daughter weighs heavier than 20 pounds, you can put her in a forward-facing carseat, but she's still safer in a rear-facing seat for as long as possible. Most "convertible" carseats will allow you to place your child rear-facing up to 30 pounds, then will go forward facing up to 40 pounds. Don't worry if your daughter's legs touch the back of the chair while she's rear-facing, even if she has to bend her legs to fit--it's very rare for a child to break a leg during a car accident and the added safety to the head and neck is worth it (if you do a search on You Tube you can find video footage of carseat crash tests, and see the difference between a forward facing seat and a rear facing seat--it's amazing--the rear facing seats are so much safer). I'd rather have a broken leg than a broken neck! The only time the child's height is an issue is if the top of the ears are higher than the back of the carseat, because then it's not supporting the head properly and you'll need to get a bigger seat that can accomodate a taller child.
So, to sum up--at this point your safest option is to get a convertible carseat that goes to at least 30 pounds rear-facing (there are some that go to 35 pounds, I believe) and then will go to at least 40 pounds forward-facing. Keep her rear-facing for as long as possible, then when you do turn her forward-facing keep her in the 5-point harnes for as long as possible. Don't use a booster seat until at least 4 years and 40 lbs, and make sure the top of her ears are never higher than the back of the seat so that her head is properly supported in the event of a crash. And have your seats profesionally installed--something like 80-90% of carseats are not installed properly.