You work from home so your energy bill sounds OK to me but an energy monitor and turning the thermostat down will help, as will putting on a sweater.
Cheap clothes are false economy and and you need to dress for the salary you earn.
Stop sniping and find out where your money is going, your household has a fantastic income and you need to look at your outgoings together. Work out your household budget, and split the remainder into 3, savings and some independent spending money for each of you.
It is cheaper and less time consuming buying washing powder, nappies and toilet rolls in bulk from cash & carry type places but you do need the storage space.
Personally I combine cash & carry with Ocado deliveries you could have 2 deliveries a week as their minimum spend is £40. I find staying OUT the supermarkets saves me lots of money.
If you prefer to shop in person try aldi or lidl. There is no reason you should spend more than £100.
With 3 small children I doubt you are using shopping as a hobby but again stay away from the shops if you want to save money.
Your have good household income but life is expensive for you at the moment, work at reducing your debts, when the children go to school you will have far more disposable income and you work to hard to just watch it disappear.