Correct. It's the value of the goods or services that count, not the amount you paid.
To answer the OP's question I would also recommend getting a credit card for reasons outlined by other posters, unless you are likely to go bad and buy stuff you can't afford. I only buy things with my credit card if I know I can afford to pay for it another way and I always pay the credit card bill in full (except if I have a 0% offer on purchases).
Otherwise you would probably be covered if you buy with a store's own interest free credit deal. The documentation will tell you if it is covered by the Act.