oh wow, i can't imagine trying to cope with this AND being pregnant, you must be exhausted.

the only thing i can think of is to have a number of baby gates (we had four of these, on four different doorways, in a rental property).

he sounds a very clever cookie, to be dragging stools, steps and kitchen chairs to help him climb up.

Placement of the things he likes to dip down the drain, in view of "could he reach this, if standing on a chair".
Put the items in the rooms, that babygates stop him entering.
You might not be able to leave hair products in the shower, if the current position is so easy for him to get to. you can get product racks that hang OVER shower doors (to hold the hair products). would that be high enough to stop him?
Otherwise the only thing i can think of is, keep the hair products in a travel toiletries bag (in a room with a child gate on the doorway) and take that bag in and out of the bathroom WITH you, when you have your shower. Inconvenient, but may be cheaper.

i'm prolly biased about the child safety gates cos i have/had such a short child, who never climbed them, got past them. I don't know what i would have done, without those gates, they were my sanity saver - and kept bilby safe.