In response to your message, there are a lot of wheels that will fit from 16" up to 19". 17" and 18" are what is recommended. Many on the forum are more knowledgeable on correct wheel fitment than I am, so a search of past posts or asking here about a specific wheel set would be good.
For a quick reference on Porsche wheels, I like to look here:
944racing
Some info is missing, but the info there is good.
For the cars I have modified I often look at wheel-size.com to reference what the stock size and offsets are. With a conversion to studs and a variety of spacers, I can make a lot of non-standard wheels fit. I'm pretty sure that the offset range shown in their charts is correct:
https://www.wheel-size.com/size/porsche/boxster/986-1996-2004/
One car I have came with 20" wheels. My wife really liked the appearance (her car), but they are heavy and did not ride as well as smaller wheels.
Maybe you could get a cheap set of wheels from Craigslist or Facebook Market to have on the car temporarily while you send your wheels to be professionally done. You could keep or resell them afterward.