If you can't afford to replace the Bitcoin you're spending, then you don't need the item. You can still get it if you want, but if you didn't Bitcoin and don't replace it, then you're spending savings. Which is fine, that's what savings is for ultimately. But I would recommend to only spend savings on things that improve your life in a meaningful way, like vacation, travel, or a productive asset like starting a business, or great utilies like a home or a car.