Re: what kind of line?
That is a good question. The floating line is the most versatile line for trout fishing. One can fish dry flies, as well, as wet flies.
Another reel/spool with a different line will offer you another avenue to catching fish. Sink tip lines will allow you to get the fly to a desired depth and have good line control in moving water. A full sink line will allow you to get the fly to a desired depth without having to deal with topwater influences (like waves) in ponds or lakes.
Another option to consider is using sinking leaders. They come in a variety of lengths and sink rates. A simple loop to loop connection between line and leader is all it takes for a leader change. This setup gives you the advantage of being able to have a quick change without having to replace a reel or spool.
Visit your local fly shop, so you can get a better feel for your options.
Welcome to the forum.