May I suggest a size where the sudoku grid is 9 by 9, but each cell corresponds to 8 (2 by 4) cells in the minesweeper?
Or what about 6 by 6, but each cell corresponds to 4 (2 by 2) cells, allowing for up to two mines in each cell?
What about allowing a different set of digits, e.g. a 4x4 sudoku could have the digits 0, 1, 3, and 4, or maybe 0, 2, 3, and 4?