Hello and Welcome to the wonder world of OB
Here's some UK links you may find useful.
Orchid Accessories
BOGA Links
Welcome to Easy Orchids
All sites above have Info and useful links to boot
Be careful of what fertilizer you use as some may not be good for Orchids. I did find in my local Booths market a bottle of Baby Bio Orchid food, Pink Bottle, though it does say on the label on to use when plants are actively growing cost about £2.
A rule of thumb to remember with fertilizer is "Weakly Weekly", with a Flush watering once in a while if/when required.
B&Q do sell Bark mix, but it may not be suitable. Usually when I've perused a B&Q the Bark is on the large and seems to be more for the Garden than pots. May be wrong though! I did use it myself, because I had no other option and soon changed when I got the chance. The difference was noticeable!
Hope that helps a little and once again
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