Don't rule out the Canon M series of mirrorless cameras or even the Canon RP.
BONUS :)you can use your existing lenses with the appropriate adapter.
Other systems worth looking into Olympus/ Panasonic 4/3 for a truly lightweight system Like the Canon M series.
For my mirrorless venture I went...
I must say if you want a more experienced flashlight photographer Phil V is your man with a vast experience and knowledge in this area.
He is always welcome to answer any questions and help fellow togs.
What’s your budget regarding a speedlight ?
I have slowly switched over to the Godox flash system
For less than £100 you could purchase either TT350n TT685n unit I have also seen both of these complete with the off camera X1Tn trigger.
One of the Big pluses with Godox is cross compatibility...