Single Long vs Single bed sheets

When I moved to Japan, I was given a foam mattress and a bed set, which came with a pillow, a comforter, and a like smaller comforter that goes on the bottom.

I want to buy sheets for the bed. My foam mattress says it is a single, so I would assume my bed set is also for a single. Well, the store across the street mostly sells sheets for "single long" beds. Would those sheets fit my bed? I don't want to buy it, just to have it not fit at all.

Also, what should I be looking for when buying sheets? Any tips?

You can have a piece of box sheet and/or flat sheet.

A piece of box sheet is something like this.
http://www.nitori-net.jp/shop/goods/goods.aspx?goods=7514778
Once you fold it inside, the sheet doesn't move. This is popular sheet for beds(Single - King size).
The typical box size sheet is 100cm(W)*200cm(L)*30cm(H). You can measure your bed before you buy the sheet.

The flat sheet is something this.
http://www.nitori-net.jp/shop/goods/goods.aspx?goods=7514552
This sheet is used mainly for "Futon" but you can use it for beds.
There is no "height", while it's "flat" and a piece of fabric, so you can fold any shape you want. The typical flat size sheet is 150cm(W)*260cm(L).

I don't think I've ever seen sheets for sale that don't specify the measurements. So you can first measure your bed, then make sure that the sheets are bigger.

When buying sheets, comforters, comforter covers, etc., I've found that Ikea generally sells larger sizes than most other shops.

A single long mattress is a little bit longer than a regular single mattress. When looking at Francebed's sizing chart for hotel beds the length of a normal single is 1950mm while length of a long single is 2030mm. So the long sheet would be a little bit too big for a regular single mattress.