Eugene baby stock them but I am sure you can find them at any bigger baby shop. There is such a huge variety of designs and systems that it might seem quite confusing at first.
I personally use Imse Vimse organic cotton diaper covers that are super thin, waterproof and super easy to put on. I have just two pairs, which I find more than enough as I don't wash them more than once a month as they don't get wet anyway.
And then I use muslin squares to fold inside. I find them easy to use and very easy try in this high humidity environment. I have 15 squares. If I use just cotton nappies the while day I use about 4 ot 5 during the day so then wash them every other day but usually i use them just half day (and use disposables when going out and during the night) and then it is enough to wash them about once a week.
I also purchased fleece liners taht might be very handy if you can't change the nappy that often and your baby does mind feeling wet (i.e. at night or for day trips) but I don't use them anyway and change the nappy more often instead. I think the liners can be very handy for separating the solids also but as I mentioned in the previous post I don't have this problem.