Either olive or coconut oil plus honey or another sugar source is a classic combination that is raved about, check out YouTube. But if you have a conditioner base with a lot of oil you could just add the honey, if you have one with a lot of humectants you could just add the oil. Let us know how you get on!
Be aware not all oils will penetrate the hair, anything polyunsaturated will likely not. Coconut can if left long enough, probably also olive and avocado, you might not get much penetration tho being low porosity. There is a series of excellent articles by 'curl chemist' Tonya McKay where she explains the function of different ingredients.
Tonya McKay | NaturallyCurly.com
2a-2c, medium texture, porous/ colour treated. Three years CG, growing out mechanical and chemical damage = breakage and very high porosity. Past armpit length heading for waist.
Treatments: Komaza protein, Komaza Matani, coconut oil with sugar syrup. Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume
Styler: Umberto Giannini jelly, Boots curl creme, Rockin RInglets
Experimenting with: Mega-Tek, Curl Harmony reviver, Elvive Full Restore 5.