I've used Caledonian Sleeper a few times to go skiing in Scotland. As well as Aviemore there are good bus connections at Spean Bridge for Nevis Range and Bridge of Orchy for Glencoe. One of the reasons I go down that route is the ability to cancel until 1 week before. My general experience is that daytime trains at that point are too expensive for me to consider. So I often take a put on a couple of sleeper tickets. Though sometimes even a week isn't enough notice for the Scottish weather!