Two dimensional matrix-like data type using lists and/or mutable lists

I am trying to think of an implementation of a two dimensional matrix-like data type.

Normally I would take an array of arrays but I'm bound to a relatively low language level which only provides lists and mutable lists.

So of cause I could take a list of mutable lists and, in search of an item in row n and column m, get the m-th mutable list and go throught it until position n. But isn't there a better solution than going through the whole list?