looking for an object that works like a classical 2D array:

f array n[][] = {{1, 2, 3;};
{4, 5, 6;}}

and is accessed by telling it the coordinates where to read / write a value (float or int would suffice).

arrays in Pd seem to only work 1D, assigning 1 value to 1 position?

yes, arrays are 1D, like lists.
have a look at [matrix] from iemmatrix lib (pd-extended).
but its possible to select values by row + column in a 1D array also.

I often use [msgfile] for things like this, though this is probably not be the most efficient method.

thanks! just messed around with [matrix] for a few hours yesterday and it's exactly what I wanted.

I'm a bit gutted it outputs it's contents everytime you fill it - of course, I only want it to output when I send an [element], [col], [row] etc. command.

I got around it using [t f] on the output, but that gives me a (non-lethal) error when it receives a matrix variable. outputs the floats alright though

Instead of [t f] you could use a [route float] to filter the output.