I think you need to pin down "near to Denver" in terms of travel time. If you need the services of a city, Denver isn't the only choice, as urban Colorado sprawls along I-25 from Fort Collins down to Colorado Springs. This is all on the plains at the foot of the Rocky Mountains, so for climate, you might as well be in western Kansas.
Cool in the summer? You need to define that. The plains east of the mountains get hot, hotter than any place in Florida, but not so humid. Once you get to 7,000 - 10,000 feet elevation, you might find cooler temperatures, particularly at night, big swings from day to night. But high altitude communities could be a couple hours or more driving time from Denver (or Fort Collins, Pueblo, Colorado Springs).
Places I like in Colorado? They are all in the mountains of southern Colorado. I've been in the Rockies of northern Colorado, the appeal is just not the same for me.
The towns in the Rocky Mountains are high enough to have a chance of being "cool" but not as cool as northern states. I like South Fork to Durango, along US-160. Gunnison to Montrose, along US-50. Durango to Montrose, along US-550. But in this area, if the local cities are not enough civilization for you, it can be a long drive (6-9 hours in good conditions) to Denver or one of the other larger cities along I-25. I have friends who live year-round in Durango, they find it big enough for everything they need, but their mom prefers a condo in Denver.
Are you thinking about winter? Colorado mountain winters can be really nasty, and while it can be OK to just hunker down for the season, a RV might not be the right place for that, if you can find a RV park open. For most of the mountain areas, the season runs to about the beginning of October, then a month or two later things start getting into swing at winter sports resorts, some of which are same as the summer resorts, some in different places.
The climate part is tricky. Canon City, where the Arkansas River starts cutting the Front Range west of Pueblo, is at 5300 feet. Summer average highs are in the high 80s to low 90s, but extremes can be 10-15 F higher. Montrose, on the west side of the Rockies at 5600 feet, has summer highs averaging in the mid to high 80s. Durango, at 6500 feet, has summer highs averaging in the low to mid 80s. Estes Park, at 7500 feet, has summer highs in mid to high 70s, but extremes can be 20 F higher, and the nightly lows within 10F of freezing. Get down on the High Plains at the edge of the Rockies, summer temperatures may not be much different from those in Orlando, although there may be wider swings between extreme highs and lows.
