Welcome from Boulder.
NoCo feeder supply (FC) is having a beginner chicken workshop this Saturday. She carries the best selection in the front range typically 25+ most times of the year. She will normally have close to 1000 chicks available this weekend plus specials on feed. Well worth the drive.
As far as breeds that do well here most are fine. Personally, I like to stick with dual purpose small comb breeds. Barred rock, easter eggers (green eggs) ( incorrectly labeled as Ameraucana at the feed store), Wyandotte are a must in my flock. Other nice breeds are Orpington, Australorp, brabanters ( white egg), Sussex, welsummer (dark brown) plus a few eye candy breeds russian orloff and Cochin. I do stay away from RIR as they have a reputation as bullies in a mixed flock and hybrids as they are typical spent (poor production) by 2. I have 6 year old DP hens who still produce 4 eggs a week.
Wardles will carry a decent amount of chicks and will also sell pullets. Never bought from them.