Tailored tutors does look good, but it is expensive particularly if they one cover one of your subjects.
I really liked The GCSE Maths Tutor too - he does have an A level series on pure maths which is probably worth a look over summer.
It is good you are planning ahead, but I will say again to wait before you sign up. I get loads of work set by teachers and wouldn’t have the time (or need) to do extra via a paid platform regularly.