With my DD, I was told that I absolutely had to have a bassinet and a crib, and that a co-sleeper would make night time feedings a lot easier. So I got all three. DD never so much as took a nap in her pretty little bassinet. It turned out to be just a decoration in the nursery (which was also pretty pointless). I spent the first week using the co-sleeper on and off since it was right there, and I figured I should get some use out of it. By the end of that week, I took it out of the bed. I made a few half-hearted attempted at using the crib, but we both hated it. In the end, all three items were a big waste of money.
With my DS, I knew we would co-sleep 100%. However, we were in a DV shelter when he was born, so I got another little co-sleeper like I had with DD so that it could be said that he had his own sleep surface. Though we've never actually used it, I kept it regardless for a long time, because it folded and took up very little space, and had a CPS issue come up, I could pull it out of the closet and use it to show that he had his own sleep surface. Other than that, I had no use for it, but it took up too little space not to hold onto it just in case. After he was a little older, we got a crib mattress to pull out for solo naps occasionally.
If I ever have another child, I doubt I'll bother getting anything other than a crib mattress for naps, if that. I like for DS to be able to get up and move around when he needs to do so, instead of having to cry until I let him out. If I'm not in bed when he needs something (like a diaper change or to nurse), instead of crying, he just hops out of bed and comes to get me, and he's done so since he started crawling. I also like not having jump out of bed as soon as he wakes to get my crying babe out of crib. We skip that and go straight to morning cuddles. However, my bedroom is the family bedroom (fully baby-proofed) and the only parts of the house that aren't totally child-friendly are gated off so he can't get to them without me. If that wasn't the case, I'd likely be more interested in something like a crib or playpen.
What you should do really depends on what works for you and how you see handling things later on down the road (such as when baby becomes mobile). If it isn't going to be safe for baby to roam around upon waking (or you just aren't comfortable with it), you might as well get a crib or playpen. If you're unsure but want an alternative sleep surface available, you can always get a crib mattress for now (which you'd need anyways if you get a crib) and get a crib later if you decide it's necessary.