Math Studies is a bit dangerous. I would generally recommend HL Maths for Oxbridge Medicine.
The U.K. doesn’t use the UMAT.
The BMAT Section 1 tests problem solving, understanding argument, and data analysis and inference.
Section 2 is based on the knowledge typically included in non-specialist school Science and Mathematics courses. It tests your ability to apply this knowledge – possibly in unfamiliar contexts.
Some past papers are available online. If you want me to take a closer look at your candidacy send me your IB subjects in full and academic results from last year to email@example.com and I can tell you which schools are achievable