The basic technique is well explained at
http://rasamalaysia.com/steamed-fish-recipe/ Particularly the final seasoning with fresh ingredients after cooking.
I've used the bamboo steamer and it's not that good steaming a whole fish. Most of the time they're too small to fit a worthwhile sized fish. If you're using a wok, I prefer to lay four bamboo chopsticks (because they won't get weak in the heat and steam) in a tic-tac-toe pattern in the wok above the water. Then you put a heat proof plate on top of that with the fish. Cover with a wok lid to hold the steam in. The first time I steamed a whole fish, that was my set up. Works for other things too. With starchy sticky items, they should sit on a bit of parchment paper, lettuce leaf, or a round of carrot for shu mai is sometimes done.
The bamboo steamer is fine with a small plate and some fillets though.
A couple years back I bought a doubledecker 14" stainless steamer at Super China Market on 9000 South. It wasn't expensive and I don't use it a lot but it has enough capacity for dumplings, whole fish, bao and other good tasty things. The bamboo steamer wasn't big enough for groups, or even my family really. I used that this year. I had a little struggle getting the plate out as it was a tight fit. But I was able to do a fish on each level which I couldn't have done with the wok. I was using an oval plate as it fits the fish right but was perhaps a little tight for the steamer.
Super China Market has a good selection of frozen fish though you have to gut, scale and other prep yourself. How much prep varies with the fish you select.
I've steamed the regular commercial cuts (tilapia, trout, salmon) and fillets with good results too, just that the Chinese prefer a whole fish, preferably caught fresh or purchased alive. This year i did a whole red tilapia and a golden pomfret. The pomfret was quite troutlike which was a surprise.