Wheel/Rim Selection - Uncertain which to buy. Do I go with smaller wheel width, or smaller offset?

My 2018 Prius Prime with Premium Pkg has:

OE Rim Size and Bolt Pattern
15×6.5 5×100 ET40 54.1mm CB

OE Tires:
195/65R15

I just got 4 new all-season tires, same size, and kept the 2 rear tires that had less wear and were still good.

My idea is that if I get a new wheel, as opposed to a donut, and put the better of the two tires on it, then I'd have an extra wheel to keep strapped in the back as a spare on my upcoming trip.

In a few weeks, I'm going to be driving from the US East coast to the North West, down the West coast, then back East, putting around ~6500 miles on my car in a month's span. Just got the new tires put on, and plan to get them rotated once I get back. I also have a scheduled oil change, and state inspection at the dealership next week. Hoping if I get a wheel by then, I can have them put the tire on it so it's ready as a spare.

With the wheel, it's been frustrating in my searches online to find the exact match of a wheel sized 15×6.5 5×100 ET40 54.1mm CB aftermarket. The dealership quoted ~$400 for an official match, and I'd like to find a more affordable option.

The closest I've come to finding is:
15×6 5×100 ET40 54.1mm CB
15×6.5 5×100 ET38 73.1mm CB

I'm between the two options and not sure which is better and will have the most minimal impact on mileage or reliability in the event I need to use the spare. Are either wheel option within the allowable range and would be fine, and also with using the OE 195/65R15 tire size I have?

Either I go with a wheel that has a 6" wheel width against OE 6.5" width, which the other 3 will be if I ever needed to use this spare, or the other option of a wheel with a center/hub bore of 73.1mm, and if I get Hub Centric Rings 73.1 to 54.1 that should resolve, but still has an offset of 38mm vs OE 40mm offset that the other 3 would have.

Is a wheel with 0.5" less wheel width or a wheel with 2mm less offset the better choice for a spare, and could it be used more longterm than that potentially since it's so minimal?