General advice

Hello to all  newb here. will start with what is probably pretty easy question. We are living in Australia on the Aussie aged pension .So you will know we are far from rich and famous. but by not eating out or spending on entertainment we manage to have a trip to Asia every year, where we do eat out. My Son and his adult son and 6 year old have recently moved in with us.So we are considering moving to Thailand Chang Mai in particular.So I booked a flight but stuffed up the booking giving us 5 weeks to  see what living in Chang Mai is like instead of the 30 days,So at last I get to the question.Do I ask the airline to change dates and /get 60 day visa or cross the border. Im, this will give us more time to really see if this is what we want. thinking suck up the excessive airline fare and go the 60 days one way or another.Any advice will be gratefully received especial whether to go across the border or just pay up for 60 days on top of the extra air fare. thank you all Lesleigh