The 7ltr Luxfer cylinder  is the popular choice of most divers.

http://www.diverswarehouse.co.uk/index.php/cPath/12_536_541

The Apeks Atx40 Ds4  Regulator is well tried and tested 

With 6"/15cm  Hose

http://www.diverswarehouse.co.uk/index.php/cPath/30_414_432

As they leave the factory standard Apeks regulators are suitable for use with oxygen enriched gases providing the oxygen content does NOT EXCEED 40%*. For mixtures containing more than 40% we offer a range of regulators suitable for use with Nitrox and Oxygen (also known as oxygen enriched air or EAN - Enriched Air Nitrox). Our comprehensive range, for all you dive requirements comprises the DS4 first stage and the XTX200, XTX100, XTX50, XTX40 regulators. This equipment has been specially cleaned and assembled in our purpose built class 'J' (10,000) Clean Room using oxygen safe components and lubricants and are suitable for 100% oxygen use. All first stages are available in yoke ('A') clamp or DIN fitting. .

* Nitrox equipment will be supplied in Europe in accordance with the EN 144-3 and the EN13949 which states that equipment sold in CEE (European Community) countries over 21% and up to 100% will be manufactured with the special M26 fitting.