What is mid-range to you? The prices in CM are well below that you'll find in Bangkok (in general though that's not an effective wholesale categorization) so keep that in mind.

For Dec 25-28 period, the height of Thailand tourism, you might be limited by availability.

I personally avoid the areas around Tapae Gate, inside and outside the old city, like the plague. Though obviously many are drawn to it.

In the old city I could recommend Siri Lanna, De lanna and, as a true boutique hotel, Baan Klang Wiang. The first two are in main areas of the old city but not as flooded with tourists as you'll find east of Tapae Gate. The last one is in the southern stretches of the old city near Chiang Mai Gate and Chiang Mai fresh market.