RichardinSF also pointed this out - I've addressed it above.

I'm afraid I'm not the best qualified to comment on single rooms - I realise now that my experience in looking (almost exclusively) for rooms with semi-double beds and wider means that I haven't a clue where I can find a floor plan which shows one - certainly not a direct link which doesn't involve clicking on Japanese labels first.

Quite a few Japanese rooms do sell semi-double rooms as single rooms (perhaps more and more) so it isn't that confusing - on consideration, the Kyoto Garden Hotel links might, after all, be pretty representative of the hotels the OP may well find himself considering.

If anyone has an alternative link showing a hotel's range of rooms, please feel free to post it here. One of the few alternatives I know of is this one:
http://www.princehotels.co.jp/takana...dar/index.html
It's in Japanese and you'd need to press the green buttons across the top of the page to see the different rooms - but it's a higher end property and the single rooms all have double beds (21m2)

To be honest - I can't find any pictures of a single room in a familiar hotel where the bed isn't a semi-double. Sorry!