The best bit of advice I could give you at this stage then, is actually ask each insurance company what their view on mods is.
While they may cover it, not all cover it like-for-like, so if you crash you get a standard part as a replacement. Also, some really don't like certain types of modifications, such as performance mods. Be honest with them and ask what their policy is and work out what's best for you.
I went with Greenlight as they are happy to cover all forms of mods. For instance, it's only around £30 to cover a remap
I know other people have been quoted similar prices with Greenlight too. With Elephant, they wanted a small fortune!
Don't pick based on the cheapest price, as it may limit what you can do with your car