I would get an oral B complex supplement that contains methylcobalamin instead of regular cobalamin and that also contains methylfolate instead of regular folate. The methylated B vitamins are superior, in my opinion. They are so much more bioavailable. I don't think people even absorb regular folate and regular B12.
If you choose to use the regular B complex, make sure you have a lot of methyl donors like choline, DMG, TMG (betaine), SAM-E etc. There are many and you need them. But you can also get by with using a lot of just one methyl donor, with choline being the easiest one to use probably.