Just start expanding on your range of imperium. You can always make a mixed force army at 2000 points.
Get yourself some custodes- one box of five builds a patrol detachment of them. Two boxes and you have a battalion.
Grab a single knight box and add a super heavy auxiliary.
Oh, or maybe you like tanks and imperial guard is more you your liking- they have a huge range of dudes that do all sorts of things.
Combine that with some of your already existing marines and you could easily create a more dynamic list that is both ‘fluffy’ and viable.
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