Another option would be to include an index.
With regard to selecting currency pairs, you may like to also investigate the following thread. It is not a trading method/system as such. It is a method for identifying the current strongest/weakest currencies with respect to JPY as a base. It only considers the majors but often the actual S/W pair formed by the two extremes is a cross pair rather than just against USD or JPY. I have not actively traded this myself as I tend to specialise in EU but I do follow the thread and it seems to be achieving some significant success…might be worth a read.
https://forums.babypips.com/t/trading-the-trend-with-strong-weak-analysis/77959