dd1 is a small 3.5yr old. she has got too big for her stage 1+2 cr seat tho and need to get a new one. she weighs approx 33lb. would a booster seat be ok for her, or would a high back booster be better. she can undo seat belts easily, so i like the idea of the 5point harness for a high back booster, but just really confused. too many products/designs/styles available!!