Malawi is probably the safest country in Africa for travelling alone and you can anticipate few problems.
In fact, many travellers report that, compared to North Africa, South America and numerous Western countries, Malawi feels relatively safe and unthreatening, but you need to take all the usual precautions especially at busy bus stations, isolated areas, or at night.
There are many backpackers and solo travellers and plenty of places where it will be easy to meet with kindred spirits in Malawi, so you can easily team up with others.
A single room is usually more than half the price of a double or twin room, and many of the more upmarket, full-board lodges and safari companies apply a single person supplement.
A lot of backpacker hostels provide dorms for budget travellers.