Hi Teg2400, I personally would suggest getting a 19 inch steel wheel to have as a spare, if there is room in the spare wheel basin.
My sister-in-law has a 2017 Astra 5-door. The space saver is a 16 inch wheel, it was needed a few weeks back, and the whole response of the car was totally altered because it was sitting so low on the rear corner. She is looking around to replace it with a wheel nearer to the size she is running with.
I know the space savers are only supposed to be used to get you out of trouble, but they do make for a whole different drive, I can understand why there is a speed restriction on them.
This probably hasn't answered your question, but it may give you an option of which to choose.
Regards Andy.