We’ve been taking our one son since he was 7 1/2 months old (he’s now almost 4) with no issues.
Your son really will be able to ride most of the rides, and we never feel like we are missing out.
For the height restriction rides, using rider swap is easy and effective. If using FP+, only the person riding first will need a FP+. For example, you get a FP+ for Seven Dwarfs Mine Train and your husband gets a FP+ for Space Mountain. You will both get to ride both of those rides, taking turns while the other stays with your child. We’ve never felt weird riding alone because the height restriction rides aren’t exactly ones where you can sit and have a conversation.
We like to schedule our height restriction FP+ times around when our son should be napping (he naps in his stroller) or during a meal if we are doing counter service. He takes longer to eat, so DH and I are able to usually both ride. Example of how this works: DH has a FP+ to Avatar Flight of Passage. We all go to the ride entrance (they need to see the child too short), and DH tells them we need to do a rider swap. He is given a rider swap lanyard, and when he gets to the second FP+ checkpoint, it is exchanged for a rider swap paper pass (similar to the older paper FP). My son and I will go to Satu’li Canteen and order lunch for the three of us. After riding, DH meets us there and has his lunch with our son while I go and ride with the paper pass.
A couple of things to keep in mind: You do not need to use the paper rider swap pass immediately. They usually expire at the end of the month (it will say), so you can ride later in the day or later in your trip.
Single Rider Lines: Expedition Everest, Test Track and Rock n’ Roller Coaster all have single rider lines. In our experience, these lines are most effective for Expedition Everest, okay for Test Track and hit or miss with RnR. If you do Test Track, the parent waiting can enter through the exit and go through the gift shop to the car display area. My son loves sitting in the cars while we take turns riding, and it’s also a nice break with the a/c.