Traveling Internationally

Hello! In a month I will be traveling with my husband and our 4 month (5 month at time of travel) old son to Copenhagen. My main question is about strollers. I was thinking about getting a used travel stroller to bring so we don't have to worry about something happening to ours - we only have one that works with his car seat. Since I don't know if he will be sitting up on his own at that point, will I just have to use ours with the car seat attachment or are there travel strollers for babies younger than 6 months (that aren't super expensive)? I've been looking on google but there's so much out there and I usually get more info from people's experiences on reddit anyway. Also if you have any travel tips I'm all ears! He's generally a pretty content little guy and travels well but I'm nervous about flying of course.