Moontjuh22 Since sims are freezing to death, I assume you have Seasons. So, sims will still freeze and die if there is no heat in the house. To fix that, install a thermostat and adjust the temperature. You will have to change the setting of the thermostat depending on the season and which world you are playing in. So, turn it to heat in the winter and to cool in the summer. You'll know by the buffs on the individual sims when they get cold or hot so you'll know when you need to adjust the thermostat. You can avoid sims freezing or overheating altogether for children and above by buying the buyable traits too but that doesn't help when you have toddlers or infants since you can't buy the traits for those life stages. You have to spend reward traits to buy them which in a lot of cases, children and teens won't have earned enough points for the purchase either. It really depends on how you play. If you work towards completing a lot of aspirations, you get a lot of reward points. If you play differently and don't chase aspirations, then you won't be able to buy a lot of the buyable traits.
Hope this helps.