As irmar suggested using coconut oil is very old remedy, it is good for scalp and dry hair end. Massage it gently in scalp and then dry ends leave it several hours, I would not sleep in it, cause it would grease my pillow, you could wrap the head in plastic and then in towel because it gets warmer and therefore, I would imagine it's working better, then wash with gentle shampoo.
I would not use olive oil because you won't be able to wash it out well, I used castille soap as shampoo before and it left also an oily residue on my hair as well
As hair tonic /rinse you can use a apple cider vinegar with the mother (organic, unstrained) mixed with some water, you can also use old kombucha (which will turn into a less acidic vinegar). You could infuse the vinegar/kombucha vinegar with sage and rosemary, just put herbs in the jar for at least a month to extract the oils.
Vinegar rinse detangles hair and is pH balanced.
Here an excerpt from mountainroseherbs:
Hair rinses are simple to make, and they naturally condition the hair and scalp. They soften, add shine, body, and enhance natural highlights. To create an herbal hair rinse, simply pour 2 cups of boiling water over 3 or more TBSP of dried organic herbs (see list below) and allow to infuse for 8 hours or overnight. Strain herbs from the liquid, you can gently warm the liquid if you’d like. To use, slowly pour the rinse over your head, making sure to massage the infusion into your hair and scalp. Keep a large bowl under your head to catch the liquid and reapply. Repeat several times, and either rinse out or allow to dry.
Herbal Vinegar Rinse
Vinegar rinses have the same advantages as water-based hair rinses, and they also help restore hair’s pH balance. Vinegar is beneficial for oily hair, itchy scalp, dandruff, dull hair, and other scalp conditions. To make, place 3 or more TBSP dried organic herbs (see list below) and 8 oz organic Apple Cider Vinegar in a glass jar, cap tightly, and infuse for 3-6 weeks. Shake the jar daily. Once infused, strain the herbs out. To use, apply 1-2 TBSP herbal infused vinegar to damp hair and scalp and thoroughly massage in, then rinse out with water. Or, you can use the method described above by combining 1 TBSP herbal vinegar with 1 cup water, followed by a thorough rinse with plain water. The infused vinegar will keep for at least a year if stored properly in a cool and dry area.
I have used Shampoos from Nature's Gate (they have now different ingredients) but still without the harsh chemicals and
by Aveda the Rosemary/Mint https://www.aveda.com/product/5311/16530/hair-care/shampoo/rosemary-mint-shampoo
I personally also think it depends a lot on the water quality you are washing/rinsing the hair with!!
I have made a mask with eggs and lemon and honey and few drops coconut oil.
You can like Irmar said do an avocado mask and there is also one with banana
or with both and/or egg, google online and you'll find all kinds of stuff!