Convertible Car Seats

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Our son is 3.5 months old and tall for his age so we're looking into convertible car seats. We won't be purchasing one till September most likely. We currently have the Mesa infant seat and love it! So far we've been looking at the Nuna Rava, Maxi Cosi Pria 85, and some Britax models, with safety being our main concern. Any suggestions would be appreciated!