How to stop Lightroom from creating new copies of my original image every time I import new photos?

If you start with newly taken photos (written onto SD card, or whatever, by the camera) then those will need to be moved or copied into normal computer storage. You can copy those into computer storage first yourself (or move them - but people usually copy), manually creating the folders required, and then import them to LrC as a separate "ADD" operation - that import selection does nothing to the files.

Otherwise you can combine the separate Copy then Add into one operation. This means LrC uses a Copy import to bring the photo files directly from the camera card into their appropriate final locations, while also importing them there.

The destination of this copy can be largely automated, through the very simple groundwork of making an import preset for each different requirement. In my case I have just one requirement: an auto capture-date-based folder tree into which all photos go - so only need one preset. that enacts unvarying, constant import settings which take account of each different photo's date, create a folder as needed, put the file in there, and import it.

Expanding on this: if you want to differentiate between clients with a top level folder, you can make and (each time) reselect import presets specific to each client. Each sets the client-related destination, perhaps also file renaming, metadata template, batch keywording - so that each photo starts out within the Catalog already located and characterised suitably for its particular Client.

Then the "Organize by" option considers what kind of subfolder organisation you want LrC to help you manage inside that (say) client-related folder. Several options: one is to have LrC automatically implement a Date based hierarchy just for that client's photos. Then once imported, doing this from within the Catalog, perhaps rename the automatically-named "date" folder adding text for the particular shoot.

Also you can check an option "into Subfolder": then type in each time, whatever new foldername you want (inside the common starting destination) for this import. That is created on disk and the files go inside there according to whichever Organize By option you've got selected. Perhaps "into one folder", meaning they all copy straight into this new folder without any further subdivision. Or you may want to reflect the different folders they are in on the camera card.

Re-selecting an import preset gives you a consistent, tried and tested starting point. This fully clears however the prior import session was set - so, no surprises. And no 'micro-management' by you.