J.H.
I saw a post on here one day that a lady suggested those noodles that the kiddos swim with putting it under one side of the mattress so it elevates it... That sounds like a super smart Idea to me and will keep the little one safe. I defiantly would skip the toddler bed Because then you have to transition again in a couple of months.
We had one of those tents to keep the cats out of my sons bed. They worked well but I was always scared to close it when he was in the bed if I had to get him out super fast I felt like it would take me twice as long to fumble with the zipper...( I think I thought to much about it).
Make it a big deal for her. Let her help with the whole process the new sheets,blankets. Maybe even take her to Build a bear and let her have a new bed buddy that will be with her at night. Then do everything like normal your night time routine. I agree about not getting in the habit of you staying in the room with her till she sleeps.
Good luck