Old house with cold double brick walls

Hello All

I know this topic has been discussed at length but I would like to describe my particular situation and get some thoughts from the experts on here.

I have a 100 year old single story double brick house on the upper north shore of Sydney and in winter the house gets very cold. We have put new insulation in the ceiling and under the timber floor (we have a crawlspace) an it did not have a noticeable positive effect. I would like to also replace the old single glazed timber windows too.

I then purchased a thermal imaging camera (this was back in august) and that provided an interesting insight. By far the coldest surfaces - colder than the windows - was the inside of the external double brick walls, just above the skirting boards - from memory it was 10 degrees (and this was while the heating was on and set to 18 degrees in the small bedrooms).

This has got me looking at blow-in insulation - rookwool etc - such as companies like Just Rite do in Sydney.

Am I on the right track? Is there anything else I can do such as something in the crawl space?

Any advice based on facts and\or experience appreciated!