Kaytee, what specific Britax seat are you referring to? I'm familiar with their products and none are referred to as a toddler seat, but generally speaking, when people mention a toddler seat, they're talking about a convertible car seat that goes both rear and forward facing. Britax does have harnessed seats that forward face only (the Regent and Frontier), and you're right, they wouldn't be a good choice for young toddlers.
Samy27, Good for you for keeping your baby rear facing! The bare minimum requirements for turning an infant forward facing are
12 mos. and 20 lbs, but longer is even better. Rear facing better protects the head, neck and spine during a crash. The AAP and safety experts now recommend babies stay rear facing until they outgrow the rear facing limits of their convertible car seat.
More info:
CPSafety - Your online child passenger safety resource
Don't worry if the child's legs are touching the back of the vehicle seat. There are no records of broken legs, but even so, broken legs are fixable, a broken neck or spine is not.
I also like the Britax Marathon, but there are many choices available on the market. Whatever you get, be sure it has a 5 pt. harness and a front harness adjuster. Do not get one with an overhead shield. A 5 pt. harnessed car seat is the safest choice.
CPSafety - Your online child passenger safety resource