I have bought as much ECO-WOOL as I can afford (it was on BOGOF at B&Q) and rolled it out on top of the other insulation in my loft. It's lovely stuff to handle - if you wrap it round yourself you can feel how warm it is! I have stapled THERMAWRAP general purpose insulation (it's a heavy-duty, reflective bubble wrap) to the rafters, making the loft feel like a space capsule. My photo (attached) shows both these types of insulation fitted in my loft
We also have an extension with an enclosed roofspace. I have filled this to a depth of 200mm with loose insulation called WARMCEL 100, made from recycled newspaper fire-retardant. As well as keeping the bedrooms warm, this has the added benefit of deadening the sound of the aeroplanes that pass over my house as they come in to land at Heathrow airport.
I have replaced my old boiler with an A-rated condensing boiler from BUDERUS (same company as Worcester Bosch).
My most expensive investment in keeping warm without wasting energy was a whole house ventilation system with 90% efficient heat recovery, from ADM SYSTEMS. This gives us clean (filtered) fresh air 24/7 while the windows remain firmly shut, keeping the warmth in and the noise out!
I have also installed a solar water heater which provides enough hot water for all our showering and washing up during the summer months.
In the year since this I made all these changes, my gas usage has dropped by 23%, saving over 4 Megawatt-hours of energy and avoiding 800kg CO2 emissions annually.
The total cost of installing the condensing boiler was £2500, the same price as installing the solar panel with a new, dual coil hot water cylinder. Having the heat recovery ventilation system professionally installed cost me £4500 and the insulation cost me £500. So I have invested £10,000 in more efficient heating - paid for by selling my car!
It won't all be paid back in reduced energy bills but I did it in order to reduce my carbon footprint. With no car, my total greenhouse gas emissions are about a quarter of what they were a couple of years ago!
These investments have also increased the value of my home so I will see some benefit when I sell up and the emissions reductions from this house will continue indefinitely, whoever is living in it.