In reply to Lykul:
Schoolhouse Ridge is a good suggestion.
Some other winter mountaineering / Grade I-ish things would be:
NE buttress of Stuc a' Chroin
NE side of Cruach Ardrain
NE side of An Stuc
Beinn Fhada ridge onto Stob Coire Sgreamhach
E ridge of Stob Garbh (Cruachan)
For something a bit more challenging, Sron na Lairig (Winter) (II) is a fairly straightforward Grade II.
(Note that you won't find any Grade I mixed routes in the SMC guidebooks - for some reason they took a policy decision that mixed routes start at Grade II !).