Warmer Sleep Sack to Save Heating Bill?

Is it terrible to just buy a warmer tog sleep sack and keep the thermostat lower. For some reason my daughters room is cold (coldest in the house 🙄) it’s winter and I have been keeping her room at 70 degrees with her 1 tog fleece blanket and footed pj’s. But our room is like 73 and I’m sweating at night. So I’m thinking get her a 2.5 tog and let her room get to 68 degrees. I just worry because sleep sacks don’t have sleeves so I worry her arms would be cold. She is 16 months BTW. It would save some money on hydro to!