The following book has really helped me to better understand the different types of insulation and sympathetic modernisation projects you can undertake in your period property:
https://haynes.com/en-gb/period-property-manual
I found it quite rewarding to individually research the author and contributors, some of whom operate their own businesses and YouTube channels offering their own unique advice and experience.
This book is also useful:
https://haynes.com/en-gb/victorian-house-manual-2nd-edition