Blanket or next size sleep sack

Sarah • 👼🏼 Jul 18’ 🌈💙 Nov 19’ 👼🏼 Mar 22’ 🌈💗Jan 23’

My 13 month old has outgrown his latest sleep sack. I can tell he’s too long for it. He hates to have socks on unless he’s got shoes on over them so I’m not sure he’ll sleep with them on at night. So my question is- when is it safe to give a blanket? If we do, I’m concerned he won’t keep it over his feet. Should we just get another sleep sack to get him through winter? Or is it safe to start a blanket?