A tip on how to wear a hat when your hair has fallen out. Buy an alice band (well that's what we called them, perhaps a head band, an elasticated fabric one) and wear it at the edge of your head closest to your head. Then the hat fits properly because without hair, the hat will seem too big, not filled-in enough; essentially the alice band provides bulk. Alternatively, wear a tight little cotton hat/covering/type of turban underneath it for a better fit.
Still finding hats a bit of a nuisance - they give new meaning to getting dressed in the mornings - and whip them off the minute i get home, to be replaced by a scarf, preferably silk.