Since the OP is listed as being from Carlisle, scuds and cress bugs are a great suggestion. But so are eggs flies, sucker spawn, hares ears. stoneflies, pheasant tails and certainly zebra midges as well as a lot of other flies
I usually start with fishing small patterns in winter, but agree sometimes a bugger or even a stonefly will sometimes work best.
Given the variety of flies everyone is successful with, one can say with confidence that fishing one particular pattern is not the most important thing for catching winter trout.
In fact it is not likely at all to have the fish locked into a certain insect since there are no real hatches happening. You may see a midge hatch in winter, and later on in the coming months maybe some winter stones and possibly BWOs.
Most times in winter, the fish hang in slower/deeper water so fishing slow and deep in slower and deeper water is usually best.
Fish during the warmest part of the day. The exception is when there is snow and ice in or along the streams and a warmup actually causes a meltdown, which will actually make the warm temp drop.
Fish where the fish are....sounds stupid, but I know guys that fish stocked freestone streams in winter that haven't been stocked since April....not usually a high percentage bet. A better bet would be special reg fall stocked streams, or wild trout streams, especially spring creeks and tailwaters.
Good luck.