Do not choose the tight connection between COS-DEN. Based on my experience there is only about a 25% chance the COS flight will operate on schedule and about a 30% chance it will be cancelled. I live near COS and fly several times a month for work. I drive to DEN to start all my trips because that COS-DEN leg is the first thing on the schedule to get cancelled or delayed if there is a problem anywhere in the network. If you at least give yourself the 2.5 hour turn time in DEN you can possibly drive up there in time to make your flight if the flight out of COS gets cancelled or significantly delayed. I’ve had to do that several times.
I wish I was wrong or exaggerating because the COS airport is so much easier than DEN. But I’ve been burned a majority of the times I’ve tried it.