The most common combinations for a short add-on to the Masai Mara are Amboseli, Laikipia or the Samburu area.
For your requirements of a different habitat and wildlife then without doubt I would suggest Samburu National Reserve. This is a much drier and hotter area than the Mara with different vegetation and animals. And, even the animals you might have seen in the Mara are different up here with different species of giraffe, zebra and ostrich all present (and in my opinion all more beautiful than the kinds in the Mara). The park is also superb for elephants.
Samburu, though still popular, is notably quieter than the Mara and, once away from the river, it's easy to feel you have the place all to yourself (and especially if you go into the co-joined Buffalo Springs and Shaba reserves). Depending on when you are there you will find direct flights from the Mara, but otherwise will have to go via Nairobi. If you're driving it's a long way – a 10 hour non-stop drive, so flying is the better option.
