N.,
Let me start out by saying that I work full time and then on top of that run my own business in the hours after our daughter goes to bed so I fully understand the need for more than 2 hours sleep at a time and the switch from the 5-6 hour sleeping 3 month old to the 2 hour sleeping 5 month old just about killed me.
You are getting a lot of advice from folks who clearly subscribe to the "cry it out" technique of getting a baby to sleep longer at night. This technique will work but it is incredibly difficult to do emotionally, notice each person says how hard it was and how strong they had to be. I really worry about this technique. Yes you get the baby to go to sleep but becuase they are exhausted from all the crying. They cry becuase they feel they need you and you ignore them. When you ignore them what are you teaching them? That when they have a need and they tell someone they have a need, no-one will listen. This results in learned helplessness, not asking to have your needs met. This breaks the trust you have worked to create over these past 5 months. Strong attachment in the first years of life has been shown to have beneficial psycological impacts later in life. We will never be able to meet all our childrens needs, it is impossible but why would we actively choose not to meet the ones we can?
Ask most mothers who have gone through the cry it out method what their gut instinct was while their baby was crying and they will say, to go to my baby. Even here those who are supporting this method say it took self control not to go to their baby. Why would you want to go against your mothering instinct, I feel that is a very dangerous precedent to set in the long run. The one thing my pediatrician told me before my baby was born when I asked for what advice he would give us as parents it was "trust your gut instinct and you won't go wrong". I think these are very wise words and this techniques flies in the face of that wisdom. Read what Dr Sears an advocate of attachment parenting and co-sleeping has to say about the negative implications of cry it out.
You don't have to succomb to a life of sleepless nights while your baby is in your bed keeping you up. Our 5 month old was in a cosleeper or in our bed and we loved having her there but the night time wiggling got too much and we were all exhausted just like you. So like another responder here we gradually moved her into her own crib without any great hassle. The difference is that when she cries at night I still go to her and feed her. Yes it means I have to wake up once or twice a night but the quality of sleep between the wakings is far better. I'm not being kicked, having my nose poked and my hair pulled. My daughter knows that when she needs me I will come. There is a good book called "the no cry sleep solution" which finds middle ground between the cry it out technique and the bed sharing getting no sleep which many of us love but just can't do in reality. The book uses gentle approaches to make helping your baby get to sleep easier without tears and I think for those of us who have been co-sleeping and like that model of parenting it is a nicer fit than cry it out.
At the end of the day as the expression goes "there are many ways to skin a cat". I would encourage you to listen to your gut and find what is right for you.
Best wishes,
C.