My 5 month old son has just started rolling and attempts to roll when in cot but is unable to roll all the way due to sleep suit stopping him as it is a 2.5tog which is quite thick. My questions is do I have to sleep him with his hands uncovered? His arms are out but he constantly sucks his thumb when hands are uncovered and this is keeping him awake. Also, when he rolls onto his stomach when he gets tired he will put his head down but not to the side and I am worried he will do this in the middle of the night, do you have any suggestions on how I can avoid this? Thank you

Dear Chelsea.
Thank you for reaching out to Red Nose!
It sounds like you have a very healthy baby there - all babies enjoy self soothing through sucking on their hands, this is normal, help with development, including midline orientation and it is important that we allow them to do this. All babies sleeping in sleep bags MUST have their arms free for safety reasons. 
During the day, practice as much tummy time as you can. By this age, your son should be able to remain on his tummy with his head up and happy for at least 10-15 minutes 3 or 4 times throughout the day. This will help to ensure he has strong core, back, neck, shoulder and arms muscles to help him in the sleep environment if he rolls. To further support his safety, ensure there are no loose items in the cot, no pillows or toys or anything that could increase risk to his airway. Please NEVER consider using pillows or towels or purchasing devices that restrain a baby on their back as these techniques are extremely hazardous and must be avoided.
Best wishes,
Jane