shall i get a new car seat

[tinkcantwaitfor3dscan]

dd has britax si car seat it is from birth to age 4 (18kg)
dd is 3 years old will be 3 and a half when baby comes she has a tiny frame is only 11kg so will never reach that weight by 4 and will be too tall by then for seat.
would like to use britax si for new one as from birth.
looking @ getting britax evolva 1-2-3 as from 9kg-age 11 years

we got gracco car seat for our 3 yr old ds up to age 11 and its great and not overly expensive

Make sure you get one where she can continue to use a 5-point harness until she is too big for the harness, rather than go straight into using the car's seatbelt.

We have the Evolva 123 for our 12kg 3.5yr old- it is excellent, she is still in the 5point harness and it fits her well. We have the Britax si too which is still going strong.