Do you have a comfy chair that you could move into his room for a while? That you could sit in with him held on your lap upright, face inwards? Patting his back, his head nestled into your neck?

My son Charlie was a big boy by around 5 months, and whilst he slept in a hammock he generally self settled and had no need for rocking etc, but when he was teething and needed the extra comfort/cuddles, this method worked well for us, without my arms aching! Later on (at about 10 months) with the first of many ear infections, this trick became a lifesaver.