I don't know if the lanolin would help preserve the cotton or not.
It's in a really harsh environment. Weather of all kinds, abrasion from dirt and dust particles......sorry, I just don't know. I do know that if it's not applied well then lanolin can leave greasy spots, and if they're thick, they're sticky.
I'd be inclined to try some of the rub on diy waxes folks make and use the hairdryer to disperse them into the fibres. greenland wax in the search 'should' (rolleyes, might ??) give you more details.
Techwash is good, but it's not necessary. It's wool, the bar of soap beside the sink will do to give enough lather to wash it. So will bog standard straight forward shampoo.
Lot of mince talked about pure soap flakes, really only desperately needed if folks are allergic to any additives that might be in ordinary soap bars, and the flakes dissolve easily in hot water, while a bar needs rubbed up to a lather.
We use glycerine hand soap for felting, yet the folks who sell felting stuff insist we 'ought' to use only pure olive oil castile soap. .....at ten or twenty times the price
Funny how well our felting works, isn't it, especially using cheap soap ?
Same thing with washing your wool.
Up to yourself really, but I'd go for simplicity.
atb,
M