You won't specialist in forensic pathology for a long time. You need to be interested in the breadth of medicine, as you will need to study the full range of medicine in the medical degree for 5 to 6 years, then work across the range of medicine for 2 years as a foundation doctor. You won't even begin specialising in forensic pathology then, as you'll enter histopathology core training for 2 more years and only go into higher specialty training in forensic pathology after that. So you won't be going into forensic pathology specifically for 9-10 years minimum.
So focus on just getting into medicine, and do anything of general interest to you in relation to medicine. You aren't going to be doing published research as a school student. Just do the required work experience and reflect on it, and prepare for the UCAT etc. If you have the opportunity to participate in anything more specific e.g. science fairs or similar then go for it but you aren't required or expected to do anything more than just wider reading for "supercurriculars".