We've a heat pump + very small solar panel array, A2 rated 3 bed terraced house (1930s)
We were using about 5-6000KwHr of Gas and 1000KwHr of Electricity a year (house was D rated and both working out of the house during the day). We now use about 600KwHr of gas (cooking) and 2200-2600KwHr for electricity with someone working from home everyday. So our energy use has gone down, but gas is a lot cheaper than electricity, so not a dramatic difference in bills. **We're low energy users, so figures may be very different for another family.
We went with a one stop shop as i knew it would take us forever to do it piece meal. It will never pay for itself in terms of reducing bills, but we can use all rooms comfortably now (1 was cold in winter previously with heating on ). A lot of the money we spent, we'd have to have done regardless - the windows/doors were over due being replaced and we knew we needed to upgrade the insulation / airtightness.
We'd have gotten the same comfort with a bit more control doing all of the insulation (some internal at front of house/external at back of house /attic/underfloor). But given age / life expectancy, figured do it now and get all of the benefit from it, my figuring is when retired that I'll be grateful for the heat/steady temperature during the day - Can't tell if this is a good call or not.