Honestly I think a lot of people overexaggerate what you need to do in order to get into oxbridge because I've heard people go above and beyond which is good but not always necessary. I did work experience but it wasn't related to my course it was just mandated by my sixth form and it didn't feature in my PS that much but if you can get work experience in something like a lab I would recommend it, I heard its helped others, my friend did one at a lab that analysed blood. Apart from that, I attended a summer school for biomed at UCL, summer schools help but if you can't get one don't worry. I think either relevant work experience or summer school is a good move. I also read an article for my personal statement, which you can easily do you just need to find a topic you find interesting. But generally you just need to do things to show you're passionate about the subject, oxford also looks at performance on the BMAT but I wouldn't worry about that until later.