Vitamins in isolation don't tend to particularly very well. The best source of vitamins is actually meat.[not too many people realise that.]
However, if you want supplements, the stabilised form of B1 is Benfotiamine. Easiest to get on the web. Using the whole B complex is better than individual vitamins. B vitamin are water soluble, so need to be replenished daily
Hana
In connection with leveya's question, does anyone have experience of Vitaplen from Flexicose? It appears to have B6 and B12 but lists Thiamin separately - is that B1? (Sorry to be so ignorant! I only know about Marmite!) And is this stuff okay anyway or just very expensive??
DG