A-levels are definitely a big step up from GCSEs, so I would advise on taking subjects that you genuinely enjoy a lot.
I do A-level biology and it is very different from GCSE. There is A LOT more content and the question style does get harder. It's like what I learn in a week at A-level, it would take 1 month to learn at GCSE. So if you don't really like the subject that much, it might be difficult to truly enjoy it at A-level. However, it does get much more interesting because you really learn about everything in so much more detail, so if you find it boring because it's easy, then biology at a-level would be really fun for you.
I hope this helps.