For the scalp, oily or dry, i second Kerastase (dermo calm range, blue bottles). Their serum stinks but is effective. Be careful as this is a line for irritated scalps, it will do nothing for your lengths, so condition them well. I never tried Phyto, i heard it's a good brand though. Ren├â┬ę Furterer has a shampoo for irritated scalps, it's good but doesn't do miracles either. What i use is a neutral shampoo, very soft, from Bioderma named Nod├â┬ę. Since i've gone back to it, no more irritation on the scalp, my lengths are dry so what i do is apply conditioner, air dry as much as possible, or use heat protection. I do a hair treatment with oil once to twice a week.
I would do hair masks with green clay, just apply it on the roots, and very little on the ends. You can also use green clay as a dry shampoo, or morrocan clay (it's a natural dry shampoo, super soft).
For the hair oils, coconut and grapeseed are the less expensive, some other good ones are mono├â┬», camelia, tamanu. Ren├â┬ę Furterer's stuff is mostly essential oils, you can use orange, cedar (Atlas cedar), nard jatamansi, lemon, grapefruit, rosemary, sage. Add a few drops of the selected oil in your base oil (these essential oils are have a powerful scent so test any blend you make). You can buy these in healthfood store on in stores selling supplies for homemade cosmetics. Buy everything 100% pure.
You can also get a conditioner containing them or just the pure butters like shea or mango butters, they're really nourishing and they can be used for your dry skin as well, if this is also an issue for you.
Either apply the oil all over your hair, and apply a warm towel on them, leave it on for 30 minutes, then shampoo. Or you can use just use a few drops as leave in conditioner, i really mean a few, 3-4 like the previous advice is really all you need, or it will have the countereffect of making your hair look oily.
For the dry, irritated scalp, i massage the oil well (i use a rattail comb and apply the oil just like hairdye), i also like to apply vitamin B5 (panthenol) before. It brings hydration.