Hi M.,
I totally feel your pain! I have an almost 10 month old little girl that has given us the run around with sleep. We co-slept in the beginning, but ended up moving her to her crib by the time she was 2.5 months...she moved a lot and we all started getting less sleep. But, she did wake up throughout the night to eat for a long time. Even now, especially when she is teething, she will wake up. I want to encourage you that eventually, your daughter will sleep longer on her own without all of the extra stuff. You might need to try to feed her more during the day. I offer my daughter a bottle of breastmilk after I breastfeed her just to give her every opportunity to eat as much as she wants. This might be good for your last feeding. I do think that 9pm is kind of a late bedtime for 5 months. You might consider backing it up to as early as 6:30 or 7.
I don't agree that you should give your daughter cereal in the bottle--that is highly NOT recommended in a lot of circles now. I didn't start feeding my daughter food until she was over 6 months anyway because breastmilk really is best until then.
I like what Kimberly C suggested. Since we don't co-sleep now, her advice sounds pretty practical. However, if your daughter is anything like mine, mine was crawling by 5 months, so that added a huge number of complicating factors. She'd be off that futon in seconds.
I think right now your main issue is that you are tired and your daughter is having a 4am play time. Try to sleep during the day when your daughter sleeps. (I hope she naps! Mine takes many 30 minute naps, which doesn't afford me the time to nap very well.)
It would be great if your husband could help out too, but I know that might not be possible all the time. We had a run of nights where our daughter kept my husband and I up 2-3 hours trying to get her to go back to sleep. He finally put her in her crib and we turned the monitor down. Sometimes you just have to sleep.
Here is one thought that might help you, though it might not. When we wanted to transition our daughter out of our bed, we put her in the pack'n'play bassinet. However, after a few nights of me waking up with her next to/on me, which I did not remember doing (bringing her to bed to breastfeed), we decided that we should move her to her crib. (She was napping there already.) Falling asleep breastfeeding is great and in general, I think it works for co-sleepers, just not for us. Anyway, for a little while, my husband would bring my daughter to me, which kind of woke me up enough to be aware of what was going on. (I had a c-section, so I guess I had a longer recovery warranting his help.) Eventually, though, around 3.5 to 4 months, I started going to my daughter's room and feeding her in my glider. She usually would go right back to sleep, so I'd put her in her crib and go back to bed. Staying in her room was key for keeping her sleepy and not adding any extra stimuli. Maybe you could try that?
I should note that even now, my daughter will only go to bed if we put her down fully asleep. It sucks, but that's the way it is for now. If you're not putting your daughter back in her crib fully asleep, you might try doing that. I know that sometimes babies just know when you put them down and even though you think she's asleep, she will pop right up and be crying before you can turn around. But, if you wait long enough for the deeper sleep to come, it's usually more fail-safe.
I don't really have any answers, and I guess I just want you to know that eventually some things will work themselves out. Explain to your husband how you're feeling and maybe he can take some of the responsibility for putting your daughter back down (like, if she doesn't need to eat). Don't worry about feeding her in the middle of the night. If it bothers you that much, than try a bottle of formula. I wouldn't do it with my daughter, so I just suffered through the night. :-) But my cousin chose to go the route with the bottle, and her son started sleeping long stretches very, very early. I guess it just depends on where you're at on those issues.
Oh...and the playing at 4am will pass. I've heard that when babies start learning new things they just get obsessed with them. My daughter was crawling around her crib long before we saw her do it, I'm sure!
I'm a first time 31 year old mom...so if you need to talk or live in the mid-cities area and want meet up, send me a message.