Always fully check any statements, bills etc. when they arrive
*

One degree set lower on central heating can save 5% in costs
*

Dimmer switches save electricity and lighting looks better
*

Use junk mail envelopes by sticking labels over them
*

Avoid using an immersion heater, even in summer

There again, you may not have to 'sacrifice' , take off in your new business and who knows.

But for most, downshifting is a change of life which entails a certain amount of material and financial sacrifice, so it's always a good idea to look into other things to keep you occupied socialy. Personally, I have less time on my hands than I did 10 years ago and only work about half the hours !

On the holiday side, you have to see this as often a necessity for your partner and yourself. You are spending much more time at home and working on it, that a break is a mercy.
Besides the 'last minute holiday deals' you may pick up on teletext or the Internet, consider maybe a camping holiday ? If you are unsure, borrow the stuff from someone else and give it a go.
There are all kinds of campsites in all kinds of places; the seaside, mountains, lakes, kids allowed, kids not allowed, noise curfews, entertainment, zero entertainment miles away from anything and so on.
It's not expensive and you are 'in control' of what you do and eat etc., albeit you have to buy the stuff and cook it !
Two pairs of walking boots, sleeping bags, gaz oven, tent etc., will set you back as little as £200 and once brought and presuming you take care of it, the gear will last for years.

A fine way of maintaining a 'not too regular'  visit to the local House of Fine Ale is to do the odd jobs for the Landlord in exchange for a few pints now and again.
I've cut lawns, designed menus etc and enjoyed a number of 'free evenings' through the business.

As you find new skills you will find new hobbies and if you are in a more rural situation will get much pleasure from exploring the countryside through eyes and ears which, before, never knew was there.

The good news is that in many cases people will feel sorry for you. They don't have to and you don't want that, but if asked around for a meal or a summer barbie, take them up. You may as well make the most of it !