Does it HAVE to be an ion-select?
There are a few options using CSS, Angular Material etc, at least if nothing else for ideas on the how.
some are Nasty tricks. Simply pointing you to some ideas, concepts. See what works for you and flavour to taste.
I had similar, but more “complexity” from UI team.
I used Popover, iOS style and a list, setup in a component.
Drop-down arrow from newicon set, onClick().
Job done, works like a charm and capable of VERY rich content in the “select-options”.