Check out Portseido, you can set your own base currency like GBP and it will automatically convert all your transactions to those. It also offers lots of analytics and visualizations, should be useful.
Click on insights at the bottom of the freetrade page. As good as any spreadsheet. The comparison index might not ,be suitable though but at least it tells you how you are doing and you can simply check it against an index you think is a good comparison.
Note I am assuming everyone has the same index as me to compare with IE FTSE all world index??
Am I right in thinking that?