Personally I work in insurance so can perhaps give you a few nuggets of wisdom in my experience of providing people quotes.
Insurance Group tends to be the biggest guide which i think you have already found, but also consider some ‘off the bat’ cars too.When I was learning 10 years ago, a Ford Focus 1.8tdi (Group 5E in old groups) was £1,000 cheaper than a Ford Fiesta 1.25 (Group 3 off memory).
Also you may want to consider Club Marmalade I believe it’s called?They combine the finance for a car along with the insurance.
Finally just read the T&C’s of any black box carefully.They all tend to have different terms and some also restrict the times you can drive. I have heard stories of people driving on a motorway/dual carriageway which runs parallel to a slower road and the black box believes you are on the slower road speeding.
Sorry - finally again I promise! Assume you don’t live in the Countryside/Rural area.Black boxes don’t allow for the inevitable extra/sudden braking you will undoubtedly have on country roads!