Getting deep is always a dilemma. There are different ways to accomplish it and everybody works out a method that works for them. Here are some suggestions.
1. If you are not using a weighted fly you need to. If you are using a weighted fly you need more weight. A cone head helps a lot but they cause a nose down sink. I don't mean to imply a nose down sink is bad. It is about what you want the fly to do. With lead on the body you can change the attitude as the fly sinks. If you are using lead bead heads or eyes go to Tungsten.
2. A full sinking line is the best way to get a fly deep but it is harder to cast and manipulate. I prefer a integrated sink tip line with about a 10 foot sink tip. It is easer to cast than a full sink line and the floating line helps you keep track of what the tip is doing. In a slow deep pool the sink tip will work for pretty deep pools.
Using a combination of a integrated sink tip line and weighted flies you can fish pretty deep. That is the combination I used in Alaska. If you have a favorite streamer you need to tie it with different weights for different conditions.
3. A floating line will also get quite deep with a combination of longer leader, weighted fly and split shot. By inter changing the combination of weighted fly and split shot you have quite a broad depth you can fish. This is a combination I use for nymph fishing. A floating line can also be used with streamers by varying the weight of the fly. you can also use leader sink on your leader to help sink it. The problem with that is you have to keep re-applying it.
4. Here is one technique that works well in medium to fast currant that some fly fishers over look. You can increase the depth of the fly by casting farther up stream. When you cast a streamer on a floating line across from your position the currant and line tends to keep the fly higher in the water column. If you throw more up stream the line won't help suspend the fly and the currant will wash the fly deeper. The trick is to know how far up stream to cast so your fly is lower in the water column but not washed to the bottom. I am sure most of us have cast too far up stream with a streamer and it is washed to the bottom and hangs up.
5. Coils in the line is something we all have to live with. If you are not using a large arbor reel that will help a lot.
To really keep the coils down you need to remove the line from the reel if you are not going to be using it for a couple of weeks or more. This is where the loop on the end of the fly line can be helpful. Coil the line in large coils and hang it up. Don't hang on a single nail. You need something round the keeps the line in bigger coils. If you have empty spools that the fly line came on you can wind it on to the spool. What I like to do is nail the spool on the wall and then drape the fly over the spool in large loops. The line is not tightly wrapped on the spool.
Ever so often during the season you need to clean the fly line and give it a good stretching for the full length or at least all of the line you are using plus 10' or so. When you stretch the line don't put anything in the line loops and pull on the loops. Hold onto the main line and pull. My wife is getting pretty good at holding the other end.
6. One other line you might consider is a Teeny style integrated sink tip line. The sinking tip is 24' long and has an integrated running line. It is very effective in certain types of water. It is used a lot in Alaska for big rivers.