have you tried putting someting in his cot that smells like you, you don't have to put anything crazy in it could be as simple as you sleeping with a sheet and then putting it on his bed. Being so hot at the moment if you have a large sarong you could wear it for a couple of days and then use it on the bed as a sheet, or a wrap.
You could wear a sheet around the house like a sarong for a day or two, sounds strange I know, but it might make him more comfy.

My DS now 6 months if he won't settle, we have sat on the floor with our hand in the cot and he just strokes and pats our hands until he goes to sleep.