@Rachel my partner was sleeping on the air bed the first night but he moved around a lot so the baby would wake up often from the sounds. The second suggestion could be possible
My 3 year old twins still come through into our bed when they wake and it means we all get the most sleep. They just walk through and climb into bed and snuggle up.
It will probably take Bub a bit to adjust- maybe even a couple of weeks. My daughter has slept in her own room since 6 months and by herself (she never liked to cosleep and my snoring would wake her up) and it took her some adjusting when I brought my baby back home- even though she was still in her own room with the same routine. Being pregnant with a toddler is more exhausting than having a newborn with a toddler. Your sleep and rest is really important for you physically and to be your best version for your son. I would say give it a couple weeks to adjust and see how you all go!
totally get that struggle, it's tough to balance their needs and your sleep, but if you're feeling better rested, that's a win for you both, right? Just looked it up on the 'Heal Baby Care App' and here's what it says: "It's completely understandable to feel conflicted about this transition. It's great that you've found a solution that allows you to get better sleep while still being close to your child. Gradually transitioning him to sleep independently can help; consider establishing a consistent bedtime routine that reassures him. You might also try comforting him with a favorite toy or blanket to ease the separation. How does he respond to the air bed setup? Would you be open to continuing that arrangement for a bit longer?
Can your partner sleep in with him? Could you bring him in with you when he wakes so you get half a really good night's sleep?