Chinese foam lifts on ebay usually start at 2.5cm, i.e. an inch
Best bet is to get shoes with a naturally thick heel and sole. Avoid cuban heels, they are confirmed manletcore
You can add about an inch to these without it looking suspicious. But just e aware that your trouser legs will appear shorter after you add the lift.
Better to coordinate shoe, lift, and trouser purchases; if you want long but slim trousers, you might need to get them taken in at the sides by a tailor.