Making basic soap is fairly easy, and ingredients are widely accessible: lye (sodium hydroxide), oil (olive, coconut, any will do but will affect hardness) and water (distilled/deionized). 80g lye, 200g water (distilled/deionized <- this is very important for boring chemistry reasons), 100g of coconut oil, 500g of olive oil are great as a starting base because it's close to most of the store-bought soaps while having an excess of oil (meaning you don't need to worry too much about pH or purify it further). Add lye to water, mix with oils until you'll get a consistency of thick batter (this is when you can put dyes or essential oils or other optional additives, like salt, poppy seeds or antibacterial compounds based on silver), drop into moulds and wait about a day or two. Afterwards, remove from moulds and put somewhere to dry, flip sides about once a week. Waiting time varies and depends on humidity and bar sizes, but it tends to be around five weeks. The smell during production isn't too much of a concern or problem, though I might be desensitised to odd chemical odours.

I wouldn't fuss with making my own soaps if it wasn't oddly fun, though. There's still about a fifth left from the batch I made in autumn, which is kinda comforting: no matter what, there's some soap left. ;)