There's probably a few questions you should think about when choosing your A-Levels.
Firstly, what do you want to do post-18? Uni? Which degree course? What are the recommendations & requirements? One piece of advice I have is to avoid extrapolating your academic choices and interpolate them instead. Which is to say, rather than choosing A-levels and then 2 years from now searching for courses that are willing to accept your A-levels, consider your aspirations first and then consider what subjects will be most advantageous in getting you there. If you are unsure, keep your options open, but having a rough idea will be very useful in the long-term. For example, going by your post, let's say you want to study computer science at degree level. Well then, Maths and Further Maths would be two instant recommendations, and then possible a science or economics/business depending on what route you want to go down.
Additionally, consider what you are good at, what you enjoy, and what you are likely to get good grades in. If game development is your thing, then go for it. But personally, I would only really recommend doing a subject in a niche A-level if you are genuinely considering pursuing it as a career or you think it will provide some utility to you at a later point. If you are less certain as to whether or not you want to pursue game development my personal advice would be to stick to the broader subjects (since CS still gives you enough grounding in that area. Maybe your coursework can be a game?) which retain your other options. Specialising in game development later in life is doable and in fact, most people that go into that career don't start off with formal qualifications in the subject, so not having an A-level in the subject will not detriment you if you decide in the future that it is in fact what you want to do as a career. Just to clarify, this is not me saying you shouldn't take game development at A-level, but I'm just advising that you weigh up the value of an academic qualification in the subject against your personal ambitions before making your decision.
The prior advice is good though. Attend some open days, try and figure out what you want to achieve, and most importantly try and figure out which A-levels are going to get you there.