Baby Sleep Position Concerns

Hey all,

I'm a first time mom and have a baby boy that is almost 5 months. He's a tall boy and is really about the size of an 8 month old but wears 12 month clothing. He is still figuring out rolling over and can get half way there. Well, he now refuses to sleep on his back and it's making me lose sleep out of fear of suffocation. Every time we try to put him back on his back, he either resists and stays in the position or if we fully pick him up to reposition, he rolls right back on to his side. Any advice? I'm exhausted and had to call out of work today. His nose doesn't get covered but it's so close to the mattress I worry.