Sytrax Matrix mixes great for me. I'd recommend a shaker too. Trying to mix any large volume of powder into liquid in one go is always going to be hard. If spoon is the only option, put in about 100-200ml of water, half a scoop, 100-200ml on top, mix, rince and repeat til it's all mixed in.
Most drinks with small amounts of powders are fine with a spoon, and some ingredients, such as BCAAs will never mix with a spoon. Shaker cup is a great tool to have around and they're cheap and sometimes available free.