The gear usage you describe is very wrong - it's cross chaining 100% of the time. It'll put more stress on the chain, be less efficient and wear all your drivetrain components faster. Just use the big chainring as necessary and replace when it's worn, allowing you to use more gears on your cassette and wear it far more slowly.
Yes, all Shimano groupsets come with both chainrings as separate, replaceable, removable parts, including the 105 11-speed which you have. I'm not sure why you think you need to replace the cranks alongside the big ring, but you don't. The big chainring can be a bit more expensive to buy separately for some reason, but given that entire 105 cranksets can be had for very cheap used, and in particular, un-used chainrings can be found on
ebay/Facebook marketplace for almost nothing, there is no reason to worry about this. Lots of people switch to bigger chainrings and have their originals in a cupboard.
Even new, they're not bad if you shop around:
https://www.freewheel.co.uk/shimano...MjMxNTgxJjE4ND0yMzIxNDY=#93=231581&184=232146
Even at full price, you're probably costing yourself far more in chain and cassette wear by worrying about the cost of a chainring.