A fairly simple way to make some money is to switch your bank. Despite pathetically low savings rates banks do still want our business, so why not take advantage? I have 3 accounts. One I’ve had for 20 odd years. The other 2 I switch every year. This year I’ve made £250, and my partner £50 as a referral fee. This took about an hour’s work, and probably the same to sort out any resulting issues. That’s £125/hr. I’ll keep doing it until I run out of options (most offers exclude recent customers).
You need to pay in an amount each money, usually £500-£1000/month. However it doesn’t need to be a different lump of cash. You can pay your salary into one account and automatically transfer enough into the other account. You can pay it back over if you want, depending on which is your preferred account for day to day use.