Hi Tina,
Roman gave you a great answer. Basically, you can follow that plan. If you choose one currency then add another two which will cover the exposure. If you use 3 times USD for example, you will need totally 6 currencies in the portfolio. Here is an example:
EURUSD – GBPUSD – UJSDJPY
EURJPY – GBPJPY – EURGBP
You can see everywhere we have 3 times each currency.