I recommend getting a credit card, but also keep track of exactly how much money you have, and only use the card if you already have the cash available to make the purchase. Don't borrow from your future.
But
do use the card. Use it in place of your debit card and then pay it off with the money that was already in your current account that you would have spent. This will give the credit card issuer some good news to report to the credit reporting agencies every month. The more months of "Paid as agreed" you can rack up, the better. Do not
ever pay late! And don't carry a balance. Also, make sure you get a card with no annual fee. It doesn't matter what the interest rate is, since you're never going to pay interest (because you're paying it off every month), and make it a goal to never have to pay a fee. I got a card once with a $300 incentive (!!), in the form of 30,000 loyalty points that could be taken as cash back... no annual fee, and I never carried a balance... that bank (Chase) just
gave me $300, and I never gave them anything back.
Why did your Help to Buy ISA get converted to a regular ISA? The total bonus that you could've got was "only" £3000, if you had £12000 saved up in it, but every little bit helps. If you're under 40, did you sign up for the
Lifetime ISA?
I keep a budget spreadsheet. I have a fixed income every month, and straight off the top, I put the maximum into my ISA (which gets a rather hefty for these days 3.2%), and then some more into a Lloyd's Monthly Saver.... The budget spreadsheet automatically deducts these expenses, along with a couple of other things I pay, straight off the top, and tells me how much I have left for the month. I also track
every cent I spend on the side, and the spreadsheet keeps the running total and deducts it, too, so I always know exactly what I have to play with. I am able to make saving a priority, and as a rule, I never dip into my savings (the Monthly Saver account is an annual thing that gets cashed out each spring and historically was used for visa applications, council tax, and water rates... now it's just council tax and water rates, and then I get about half of it back as a reward for being such a good person... yay, me!).
Also, I have a little bit invested in
Premium Bonds... It doesn't draw interest, but every month there's a drawing and I could win up to £1M. Once you're invested (minimum of £25 to get started), you are in the draw every month until you pull your money out, it's government-backed and secure, and you can withdraw your money at any time. Nothing wrong with stashing away £25 in the hope that you might one day win. It's incredibly unlikely (about 1 in a billion if you have the minimum invested), but it's possible.