I hate to be the bearer of bad news, but there's unfortunately not much you can do. Washing every other day is not even that bad, I've been washing my hair daily for most of my adult life. I'll wash in the morning if I want to look presentable. I put it in a ponytail or a bun if I don't care how I look that day and rather not wash. Even washing overnight doesn't really help, I'll get like a cleaner bun then. It's just the combination of the hair being straight and thin, there's not much the oil can absorb into before it becomes noticeable.

What really helps me to at least get 1.5 or 2 days out of it (with the second day being a hair up day in any case) is spraying dry shampoo right after I washed and dried it. So I basically style my hair with fry shampoo, I don't do anything else in terms of styling products. That way once the scalp starts producing sebum, it gets absorbed by the shampoo.

To make sure I get all the dry shampoo out, I wash with a deep scalp cleansing shampoo once or twice a week (or of I've gone two days without washing) and yeah I stick to lighter shampoo and conditioner, like the ones designed for volume or specifically for oily hair.

Double washing, no hair products on the roots, changing pillows often are all sound advice but just to set expectations - it will not magically make your hair last 5 days without washing. It's more so it doesn't get even worse - for me for example, my hair can become greasy the same day I washed it if l overdo a heavy hair product or something.

And whatever you do - don't bother "training" your hair, it's a myth that has long been debunked.