As unconventional as it is, my daughter never slept in a crib, she transitioned from sleeping with mom and dad, occasionally in a basinet in our room to a double mattress on the floor. This worked great for us for over a year but then I was ready for the room to feel alittle more finished and alittle less ghetto-student-ish.
We chose ikea's low malm bedframe. It only raises the mattress about 6 inches off the floor which is great for a toddler and I didn't worry about her falling out of bed since it was still very low. (She fell off the mattress twice and after 3 months in the new bed - she hasn't fallen at all).
The only problem is that the side is open at the bottom. This led to alot of lost items underneath, and since its so low it was hard to reach under to retrieve things.
I cut some wood, and painted it black. Then screwed it in place (using the kreg jig to make pocket holes) under the bottom side ledge.
It's great, we can't loose toys/soothers/snacks/water bottle etc. There is only one problem - we should have screwed it further in - so that you can stand next to the bed and not hit your toes.
A quick readjustment (using mega blocks as a square to keep the wood the same distance and perpendicular) and now its perfect.
(I just need to fill in the old hole with black paint or maybe a sharpie will do the trick)