We have a normal cot with the side off wedged up tight to our bed in a side-car arrangement. It's just like a purpose-made co-sleeper, but bigger! The mattresses are luckily the same height when the cot is on its highest setting, but it would be easy to change that if it wasn't quite right. I got a custom sized mattress made - it's extra wide so fits the whole space snuggly with no gaps. DD2 doesn't yet sleep in it, bu it gives me a safer sleep environment even with her in my bed- she can't fall out or get pushed against a bed rail. I love it! We did the same with DD1, though I just had a normal sized mattress with the mattresses pushed together by blankets between the cot side and the cot mattres. It worked, but not quite as safe.