which bed size is right for me?

Yes, but how wide are you? It's all in the width.

pharaoh, at 5'7" you don't need a bed with additional length. A standard twin, full/double, queen, and king are all the same length anyway. Only an XL twin and California King are longer.

A bed often lasts ten years. Will you be sleeping alone for the next ten years? A twin takes up the least space and if it'll do, it leaves you more floor space for the things you do when you're awake. It can also be disguised to look like a sofa, the "Hollywood bed" of the past, with lots of pillows or a backrest and a matching bedspread, so you sit on it by day, sleep on it at night.

A king is quite a large bed and many apartments and smaller houses can't fit one readily, not if you want a dresser in the same room. It's also larger than most couples need, even if they're not cuddlers.

If I anticipated not sleeping alone for the next ten years, I'd buy a queen.

Standard bed lengths vary from 79" to 80"  so length is not the issue.

The bed one chooses depends on their lifestyle and the size of the room. If you have a very small room, a king size bed may not allow for other furnishings. If you do not sleep alone, then a twin size bed is out of the question. Here are the following sizes for beds for you to decide on the width of the bed you need.

A twin bed is 39 in wide by 79 in Long

A double forward slash full size bed is 54 in wide by 79 or 80 in Long

A queen size bed is 60 in wide by 80 in Long

A king size bed is basically 80 inches Square.

There are some beds that come in XL size, which means extra-long. But you won't be needing the extra long as that is typically for people who are 6ft tall or more.

Get a queen size so you have plenty of room for 2. Even if you sleep alone you will like the extra width. 

I am 5'11", I prefer a full bed. Easy to move and works ok for 2 people on occasion. Plus the bedding is a wee cheaper.