Car seat?! Help me!

Ashley • 20, happily engaged❤❤❤
Not sure what my son weight or length is right now at 4month 12days but at 3 months we went to the doctors and he was almost 26 inches and almost 17 pounds which obliviously that was over a month ago... his feet hit the back of the seag in the car and his head is way high up.. Question is does he need a new car seat? And what are good car seats ? Any good one that go into toddler to so I don't have to buy a new one again?!