Do you even have a minimum order amount, or are you selling individual items? Because shipping isn't just about which delivery scheme you pick - it's also about your average order value.
If your products are cheap and people buy them one at a time, then yeah, no amount of optimization will save you. You either need to actually recalculate your margin, or create combo bundles so customers grab several items at once. But if your average order value allows for it, it's worth actually digging into the numbers. Calculate it precisely in a spreadsheet: how much does shipping one item cost with FBS when you're paying commission on the product price without shipping included? And how much with FBO, where your item sits in the marketplace's warehouse? A lot of people think FBO is more expensive because they see one number for storage and miss that with FBS the marketplace takes a percentage of the entire product cost plus your own logistics expenses.
Here's the thing though: if you just raise your price, you'll lose conversion and volume. Better to work with your assortment - drop or reformat items with thin margins, focus on what sells best even at current shipping costs. And yeah, sometimes it makes sense to try your own logistics through pickup points or courier delivery if volumes allow, but that's a whole different level.