Much depends on your budget. If you can afford eiderdown with a good fabric around it that is so tightly woven that dust mites cannot get through it then that is what is generally regarded as unbeatable - treated properly these will last you as much as two decades without needing to be cleaned. Musk duck down is second best. For a good one (both of the above) you will likely need to source from abroad, for example Denmark (owner's manual included). TOG is, to the best of my knowledge, a unit only known in the UK (and pretty meaningless at that in practical terms) and you will only need different items for different seasons if when indoors in winter you are subject to outdoor weather (i.e. do not heat your dwelling adequately).