10w 40 will do, make sure you buy motorcycle oil though because car oils have additives that may make your clutch slip!
This will be OK, ignore the 4 stroke claim It will be fine for a 2 stroke gearbox and It's very good value for 5 litres
http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_221725_langId_-1_categoryId_165507