I would use a fine grade orchid bark, with maybe some perlite mixed in.
I don't know what you can get there, but a company called Orchid Accessories here in the UK to a small grade bark. Not sure if they ship to Europe though.
http://www.orchidaccessories.co.uk/c...products_id=99
I use a mixture of fine and large grade with proportions of the mix depending on the orchid.
I don't have any minatures but if I did I would thing that this fine grade on it's own would be good for them.