Both of these might be too starchy, and corn presents other problems such as GMO etc. Oat crackers might also contain gluten.
Look up buckwheat crackers or make them yourself, it’s real easy. Here is one of the recipes, but there are many more: http://sugarlessstudent.blogspot.co.uk/2012/09/buckwheat-cracker-recipe.html. Google buckwheat crackers or crispbread for ideas on different varieties. You can add seeds and spices to them to make them more interesting (if you can tolerate any). Not sure if there is DM store in UK, they sell buckwheat crackers which are pretty decent and contain nothing but buckwheat and sea salt. I always have them in house and sometimes I have them as a snack, and always save a pack for emergencies when I need a quick bite.