There are two companies that I recommend in Colorado. First and foremost they serve on the advisory board for Friends of Berthoud Pass. Second, their instructors are nothing short of best of the best.
Alpine World Ascents
based out of Boulder is the Denver front range guys. They teach their on snow portion at Berthoud Pass. Which if you are getting into earn your turns backcountry, is ground zero. It also happens to be a world class spot to learn at. Local too. Markus Beck is the owner and is recognized as one of the best there is in the Avalanche field. In short, he is a bad ass.
The second outfit I'd recommend is Silverton Avalanche School
. Based out of Silverton of course. You'll do your field work on Red Mountain Pass. A proving ground with lots of avalanche terrain. I did my level 2 with SAS. These guys basically set the model by which all other avalanche schools are measured. They are that good. Ben Pritchard and Chris Landry are frequent instructors of their's. Best of the best. I am privileged to have had instruction from them.
I have no experience with Renaissance, but they do claim to teach AIARE so that is a good sign of quality.
Finally, I am not sure how big into the whole backcountry thing you want to get. I've spent over a decade playing bc almost exclusively now. Obviously I have a passion for it. Friends of Berthoud Pass
does offer free basic avalanche awareness courses and a free on snow weekend. I serve on executive team and as an on snow instructor for basic avalanche awareness. Classes haven't been announced yet, but will be soon. There are several in the Denver area. Worth a couple hours of your time and serves as a great prep for a Level I course. Also, pick up Staying Alive in Avalanche Terrain by Bruce Tremper if you haven't already. Read it before you take a Level I. You will get so much more out of the course if you do.
You're approaching this the right way no doubt. Lots to learn, but it also happens to be fairly fun to learn. Especially when you get out on snow. If you want to get out splitting at Bert and other spots, let me know.