i believe that the reason why most schools offer only
Chem/Physics for double sciences option is that if you were to
pursue the JC track in the future and would wish to get a Uni
placing, O level Physics is quite important for H2 Physics at A
levels which is important for Engineering-related courses
(which is rumoured to be easier for Uni entry). perhaps that's why
Chem/Bio is seen as the 'killer combi' (not in my opinion
though).
however, if you are ultra sure that you are not Physics-inclined
from your lower secondary experience (I believe you can actually
look at your Science Chapter Tests' results, see if you fared
better for 'Physics chapters' or 'Bio chapters'), perhaps you
should give Bio a try.
from my own experience, certain Physics concepts and formulae
that you'll encounter in Sec 3/4 are actually better explained if
they are presented using Calculus; but they're not done so as
Calculus is only introduced later in A Maths. as a result, the
concepts and formulae do not make as much sense to many
Physics students and they tend to struggle in the subject.
there is less concern regarding this in Biology; so as long as
you can understand what the concept is about, you should be safer.
Nevertheless, i agree that memory work seemed to be important in
Biology as you are required to describe many processes that occur
inside the organism in question, for e.g. homeostasis,
photosynthesis, comparing dialysis and kidney's function.
having said thus far, the decision still lies in your hand and as
long as you have made up your mind, keep yourself focused and
strive towards your target. Good Luck!