This controller tip changed my life and feel very stupid for not knowing it existed. Setting a hotbar slot as favorite lets you double tap "Y" and switch from and to the last used item hotbar.

Until I realized this existed I would have to hold Y (causing me to stop moving) to try and move between gun/sword all the while some Sandflee is hunting me down swinging madly at me. Now I can have my gun out and double tap Y to instantly have sword in hand, then double tap Y again to get that gun back again once melee is over. The key to this is picking a hotkey and marking it as "favorite" For me the sword item. Note this favorite is done on the inventory screen and while hovering the cursor over the item you hold down the right control stick.