traveling with 5 month old

So for Christmas I have to fly home alone with my 5 month old. My sister in law said she has a car seat and stroller I can use while I'm home.. my question is what's the best way to travel.. like using a carrier or should I just buy a cheap stroller that's small to use? I'm afraid he's going to be too heavy for a carrier at that age.. he's 12 weeks now and probably close to 14-15lbs. Plus I have to pack my pump in carry on cuz I exclusively pump.. I guess I'm just nervous haha need some advice from experienced mamas