You can keep it very simple by picking up a Rio Versi-tip which is pretty much a floating line, type 2, type 3 and type 6 sinktips which are 15'.

Or you can make your own like Preston described.

If you will be getting very little use out of a floating line, take a serious look at the Rio Anadramous Dredger. It is one Hell of a line...it is running line spliced into a short belly section then looped.

It comes with 24' 200, 300 and 400 grain heads. You can buy the Rio 15' heads in the type 3 and type 6 and then you would be covered for every situation that you are presented without aside from floating line applications.

Given that you are fishing a St. Aidan, a spare spool may be very hard to come by. All my single-handed steelhead fishing is done with one reel and one spool. One reel is loaded with a SA Steelhead Taper and the other is loaded with the Anadramous Dredger (along with the extra 15' tips)...it covers me for everything I need for steelhead.