Hi M.,
congrats on the soon to be new baby. My son has been in a full size bed since he was 7 months old! Did not purchase a box spring as the mattress itself is on the floor up against the wall with a guard rail on the other side. I also have his bumper pad lining the wall and a long body pillow at the end of the bed, so if he does decide to crawl off (as he does all the time) he won't hit the floor very hard.
My only issue is him crawling off of his bed during the night. He knows how to do this with no problem. My son wakes up at specific times each night, crawls off his bed and crawls to my bed to be with mommy. My solution, i moved my bed into his room. So now he stays in HIS room, but can still crawl into bed with mommy. He is only allowed in my bed if its past 5am each morning, other wise he is put back into his own bed.
I say do what is best for your family. You know your levels of safety and what you can deal with. At first i was nervous as heck having him in his own bed in his own room. As everyone was against it to begin with at such a young age. But I knew the pro's and con's of doing it. Truthfully, due to my son's sleeping schedule (it changed at 6mo), this has made a huge difference for me. I can safely put him to bed without braking my back. As well as lay with him in his own bed and sooth him back to sleep without distrubing him or bringing him to my bed.
Where if he was in a crib, it be literally impossible to do these things with. He also pinned himself in the corner of his crib all the time and would scream terrible to get help! There are many benefits to this and why i did it.
Your son is showing signs that he is ready to be in a bed. Just need to make sure he understands its his bed, and he can not get up and move freely during the night, without calling you first. That is what I was recommended to do once my son got older.
This teaches him that he has to ask your permission to get out of bed (helps during night wake up times) and not take it upon himself to get out of bed and go play. Or be in harms ways without your presence.
Good luck and there is no wrong choice in your decision!