How risky is chiang mai for an expected baby with these potential dates?

In terms of safety etc, if we were to live in chiang mai long term, and stay inside with purifiers for the 3 bad months, how much risk are we taking? The reason for wanting to move was cooler weather, lifestyle, infrastructure etc vs samui where we were living.

Baby is expected in 7 months, we don't want poor health risks for ourself or the child, but also like chiang mai a lot. Great housing options/prices too. I have never visited in Feb-April however.

My gf is thai and says staying inside those months would be fine, but I'm not sure how much that is just because it's seen as culturally more normal to have bad air. Moving date for us would be around April 5th, which I've heard is the worst and last month?