Most portcots are fairly good, they have some nice ones at the baby factory. Depends on what you want, but most will fold up nice and small (well as small as portacots can fold). As your wee man is still quite small i would opt for one that comes with a bassinette attachemtn, all of which will usually come apart and just store with the rest of the cot. Have a look around and ask the store-people about how they fold and store etc, you want something quick and easy to put up and take down with a minimum of loose pieces. We had a kingston one, just a basic thing, which we actually used as a basinette full time until our girls were 5 months or there abouts, then used it as a cot after that, granted we lived upstairs so it was warm, and they were in the cot part during summer as well.
As for the matresses, it's up to you what to get. Most will fit the standard portacot matress which they sell, Kmart has both nomrla cot matresses and portacot matresses. As we used our long term we got a normal foam cot matress and had it cut down in length to fit in our cot as the standard portacot ones are very thin to allow them to be folded and taken with.
Depends how and when youa re going to use it. our set up always fittedin our car boot with the buggy and our bags when we went off to hamilton for the week when the girls werre little, but if you're planning on travelling by plane etc regularly, you may want to consider a lighter model or arrange to borrow one where you are going.
hope that helped a little - if any.