We were blessed by our Sales guy... he fought for us and got us the winter mats included.

Options we've bought/acquired from "hand-me-downs":

• trunk-area carpet liner (the velcro-backed carpeted style one)
• cargo blocks (these: https://www.amazon.com/Multipurpose-Cargo-Organizer-Storage-Available/dp/B06VVPWSXM) You could use them with the OEM carpeted trunk, but over-time it causes wear and "tufting"... so having a liner is ideal).
• A collapsible trunk organizer (https://www.leevalley.com/en-ca/shop/home/automotive/trunk-organizers/67069-trunk-organizers) - great for storing... "stuff" (our AMA winter kit, shopping bags, micro-fibre rags, spray bottles, etc), held into a corner of the trunk with one cargo block. Regardless of how... spirited... I drive, it cannot move/shift.
• Wheel Woolies Superior Boar's Hair Snow Brush (super soft, and cannot scratch the paint, but long enough handle to clear the roof fully).
• a brass-bladed ice scraper
• Thinkware F800Pro dual-channel dashcam (salvage yard was kind enough to remove it from my wife's written-off BMW X1 so we kept it for the I5)

Bought specifically for the I5:

• 3-pak of 6-inch "credit card" style squeegees (and a spray-bottle of washer fluid) to clean of the rear window)
• small spray-bottle filled with "interior cleaner" to de-fingerprint the screens while parked... :D
• 2-pak upgraded USB-C for the center console (https://www.amazon.ca/gp/product/B096ZKFXNH) - super easy upgrade, and can charge 4 devices at once now... instead of 2.
• 12V BT battery monitoring - after a one-time issue (while the car was being wrapped with PPF, they drained the 12V and we had to jump it) - never had a problem since... :P
• ODBLink for data logging (I think it was the ODBLink MX+ ...? The one recommended by ABRP).
• 2-pak of USB LED... probably from AliExpress as I can't find the order #... stuck them in the rear USB slots for a bit of ambient lighting.

I'm using this organizer right now, but I've also used this one in the past.

Some folks use velcro blocks like this but I can't vouch for that solution. It should work fine.

I use this 39" orgranizer and use these pieces in the corners to keep it from moving.

You can put the foam at the back and the blocks in front or vice versa. The blocks velcro down and the foam can just be lifted out easily if you want to remove them.