My personal opinion - and it is only that - is that you would find 19 strings too limiting. Remember that the smaller a harp is, the less bass it will have (bass strings require length to sound properly) and the tinkly tone of playing only treble strings can get monotonous and limiting musically. (Also see my comments above re semi-tone levers.) The Early Music Shop has been going for a long time, but I have never heard great things about their harps and I lived in the UK for 20 years. However, I haven't seen them so I can't really judge. That photo is of a considerably larger instrument so it won't tell you anything about the 19-string ones.

If you're in the UK, there's a good secondhand buy-&-sell site that might interest you: http://www.affairsoftheharp.com/

Also there are the harp dealers, who do a variety of sizes: Pilgrim Harps (Surrey), Morley Harps (Gloucs or Wilts), Telynau Vining, Pencerdd, and Salvi (all in or near Cardiff), Holywell Music (London) plus a lot of individual makers, many in Scotland. If you Google using some descriptive terms you'll probably find a wealth of them. There's also The Clarsach Society (Edinburgh home base, but has branches all over the place) who could advise you. Their website is http://www.clarsachsociety.co.uk/

Get as large and as good an instrument as you can for the sake of musical freedom and variety. The smallest I would recommend would be the 26 string size (and range) that has been discussed above. And remember the old caveat: You gets what you pays for. VERY true in the harp world.