I have recently done something similar! I would recommend a Lowland, Speyside, Island, and Islay.
I would suggest an Auchentoshan 10yr or Glenkinchie for the Lowland; a Highland Park 12yr for the Island (Orkney Island); Balvenie/Glenrothes/Dalwhinnie for a Speyside; and Bowmore for an Islay.
To change stuff up, you can add an Aberlour 12yr for a wood-finished malt (sherried), to see how that affects a whisky. I might suggest this one instead of the Lowland, as a Lowland is really just a whisky that tastes like a vodka (lots of alcohol, very little flavor!)