You can create a 2d array:
TYPE mytype IS ARRAY (NATURAL <>,NATURAL <>) OF STD_LOGIC;
SIGNAL mysignal : mytype(10 DOWNTO 0, 10 DOWNTO 0);
or
TYPE mytype IS ARRAY (31 DOWNTO 0, 1 DOWNTO 0) OF STD_LOGIC;
SIGNAL mysignal : mytype;
would work, or your plan works too. You put the type...