Just need some confirmation on sizing.
Location Langley BC, January, February daytime mean temperature:36  F, nite time mean 31F
We have an in-law suite on 2nd floor open concept kitchen and family room with a 9×8 bathroom, there is a bedroom but we do not heat it as it stays between 58-65F.
Square footage to heat 750-800 square  feet.

Presently heated with 2_500 watt and 1 – 1250 watt bb heaters ( 2250x 3413= 7679 btu)
We keep the daytime temperature at 68 , nite time 62, but it takes 2-3 hours to bring it up in the morning.
If it gets in the 15 to 20 F which rarely  happens then we plug in a 1500 watt portable  heater to bring it up quicker in the morning.

I’m looking at a Gree 9000btu mini split specs as follows: cooling cap:9000(1635- 12966), heating cap:9000 (2388 -13648) seer 38, hspf 15

OR: 120000btu cooling cap 1200 (3100-13000), heating cap : 12200(3071- 18766) , seer30.5 , hspf 14.

Most hvac manufacturer sites recommend 9000 btu up to 400 sq feet and 12000 btu up to 600 sq feet .
I’m trying not to over size it as most hvac companies seem to do , looking for it to modulate so it runs at max efficiency.

Am I missing anything here? I think either one would work as they both modulate fairly low.