I must say that I have collected a few recipes over the years for smelly bath things with the intention of making them but never do. I have a recipe for rose petal bath oil:
1 cup rose petals, 1 1/2 cups sunflower oil, place petals in a glass jar, and in a saucepan warm the oil on a very low heat on stove, then pour over petals in jar and seal. Stand in sunny place for 2 weeks shaking gently each day. After 2 wks warm oil in a saucepan on very low heat and then strain through double muslin and discard petals. Seal. Put in a pretty bottle and cut tag to tie around neck of bottle.
Bubble Bath: 1 cup finely grated pure soap flakes, 1 litre boiling water, 50ml grape seed oil, 100ml rose water. In a bowl place soap flakes and boiling water mix well until soap dissolves. In a jar pour rose water and grape seed oil cap and shake really well. Slowly add this to the soap and mix well. Put into bath bottles. If mix is too thick just add witch hazel until it becomes a thinner consistancy.
Hope they work for you, or give you some ideas to start, there are heaps of recipes out there. I did find a recipe for bath cookies just before, I think on this site but not sure.