I think firstly you need to get clearer on what a credit and debit card are. There’s been some pretty sketchy advice here.
Credit card with a credit limit is essentially spending someone else’s money. They’re good as they can offer extra rewards e.g club card points, or rewards schemes. But many you can get as a low income earner or student have ridiculously high APR and if you rack up the spending and can’t pay it back you’ll end up owing a lot of money before you’ve even started out in life. They can be useful for large purchases as you can delay paying the lump sum and, as you mentioned you’re protected if the purchase falls through/goods not as described IF the company you bought from can’t refund you. But this only applies to purchases of a value >£100. Credit cards are no safer from fraud than debit cards. My husband had his cloned earlier on in the year - he suspects at a restaurant in London - they spent over £700 on it, but he was no better protected than he would have been with a debit card. Maybe less so as banks are more inclined to track and map your spending and might be more likely to recognise fraudulent transactions faster than credit card companies.
Debit cards are directly linked to your current account and money is debited immediately (almost) when you purchase things with it. Sort code and account number are used for transfers and standing orders, not purchases. Unless you own the account with proof of ID you can’t use these to withdraw money. Obviously you can only spend what you have with a debit card and there are no longer-lasting credit implications - unless you get deep into your overdraft and can’t pay it back, but you already said you don’t want an overdraft.
There are very few banks that don’t offer a bank card (not credit card) with their accounts. Exceptions would be savings accounts or children’s accounts which mature into current accounts when the child reaches a certain age - maybe this is what you have which is why you don’t have a card? If you download the banking app that comes with whichever bank you choose you can also log in and stop payments, stop the card, transfer money and contact them through the app if you suspect any fraudulent activity.
I would simply open another current account - preferably a student one - with another bank and transfer my money into it online to use for spending with the card. Then you don’t have to use cash, but your original account remains protected as you’re only transferring money from it to another account you own.
If this is too long. Basically don’t get a credit card at 18, especially one with a high APR, just apply for another bank account and use the card that comes with that.
AND if you’re worried about online fraud: DON’T buy from dodgy online stores. Keep to the main ones, use PayPal if buying from friends or unknown people (you won’t be able to use the credit card anyway as you’ll be charged for balance transfers) and be careful and responsible with your spending.