Not sleeping in cot

Have anyone changed the cot mattress? My little boy is 14 month old and for the last 5 months he wont sleep in his cot all night. He will go to bed between 7-8 and will wake anytime between 1 and 4am and will not settle back into his cot. But will settle fine on me or in my bed with me or even on the sofa. We moved his cot back into our bedroom in December to see if this helps it hasn’t made a difference so i moved him back into his own bedroom this weekend. I am wondering if his cot isn’t comfy enough for him? Or do anyone have any tips for me to get him to sleep or even stay in his cot all night. Thank you