I've been playing Scottish music my whole life and I'm a bit stumped as to what to recommend.
I think it's because there's such a vast body of Scottish music.
Since whistles can't sing songs, but play tunes, I'm considering all the instrumental as well as vocal music.
Off the top of my head Scottish music has quite a few different categories such as
-Highland bagpipe tunes. There's a vast number of lovely tunes composed on the pipes for the pipes, and an equally vast number of vocal pieces adapted to the pipes including a large number of Gaelic songs.
The tunes composed for the pipes include marches (in several idioms) strathspeys reels hornpipes jigs polkas waltzes slow airs and of course Ceol Mor or Piobaireachd. The
Encyclopedia of Tunes for the Great Highland Bagpipe contains over 9,000 tunes.
-Scottish fiddle tunes. The fiddle has always been at least as important as the pipes in Scotland and it has a vast repertoire of strathspeys reels airs etc and the "slow strathspey" which is I think unique to Scottish fiddle music.
https://www.youtube.com/watch?v=gs3J6kU_SaY-Scottish song. There are so many songs! Songs in Gaelic, Scots, and English. Waulking songs, rowing songs, milking songs, broadside ballads, Child ballads, folk songs, Robert Burns songs, songs by modern composers like Andy M Stewart and Dougie MacLean... there's no end to them.
Personally I love waulking songs above all. I even learned how to sing a few.
Here is an old recording, raw footage showing women who had spent their lives doing this work and singing these songs
https://www.youtube.com/watch?v=0CmGJ5dwBukAnd here's a modern studio recording of a waulking song
https://www.youtube.com/watch?v=TItwSyFcxgQAs far as personal favourites to play at this time, right now I'm enchanted by
Lament for Captain MacDougall. I find myself humming the lovely urlar at odd moments.
https://www.youtube.com/watch?v=ZH78VQ-v4AQ For Scottish waltzes I've long played
Chi Mi na Morbheanna https://www.youtube.com/watch?v=oZlQW4O4NpIand
Braighe Loch Iall.https://www.youtube.com/watch?v=HgglNmjHgwc