I would like to get an unbiased answer if possible for a new hydronic boiler and what brand is best and easiest to get parts and be repaired down the line?

A little history. I had many years ago (1998) changed from oil to gas. Oil boiler was installed when home was built in 1949.
I currently have a gas 80,000 or 100,000 BTU boiler, and cast iron rads. The heat never seemed right and the back rooms were always cold in the winter. During warmer outdoor temperatures the house would overshoot making it extremely hot and uncomfortable. We have learned to monitor this and then turn it off when it gets to a certain temp so that we get the right temperature in the end. I know ridiculous. hence is why I am trying to educate myself now.(I am in Toronto)

My home is a bungalo aprox 1,000 squre feet. I had a hired an engineer to give me a heat loss calculation
(42,000 Btu loss) as I was thinking of changing to forced air. I have since decided against since all of the ducting would lower my basement on an already low ceiling.

Can anyone please guide me to a very good quality and efficient boiler multi stage I guess this is more efficient?? I have done so much reading I feel lost. There is so much to know...like high mass low mass, condensing. Change to 1/2 inch piping with manifolds instead of the big 2 inch pipes. (I guess this would be fairly easy and wouldn't cause too much of a tear out of the basement which is finished).

I was personally looking at Wiel and Maclean wall mount as a quality one and what size do we get? I don't wish to waste gas out up the chimney so to speak.

Lastly as you guys and gals are pro's how do we choose and know we are dealing with good contractors (not because they say so) that will back their products and be there when we need them? What do we look for?

Sorry for the long winded thread.

Any help is much appreciated.

Thank you