Improving the insulation barrier between your ceiling and attic will only serve to increase your home’s heat retention in the winter. When it’s cold outside, the sun heating your attic is not going to increase the heat in your home more than the cold ambient temperature in your attic is going to decrease it. Before you pay to have this work done I’d genuinely consider whether there are other projects that would be much more impactful you could do instead. Definitely get other opinions from contractors first (never just get one quote for any project, prices and recommendations can vary widely) and see if you can get a certified home performance contractor to take a look at your goals