It's more a case of basic meaning than grammatical constructs.
And I really cannot see what discussion is needed - I suggest that every time you see an opening sentence of the type "So, I'd like to swap my existing 2 gang light switch..." you try a substitution, and imagine it begins "Because of that, I'd like to swap my existing 2 gang light switch in the lounge ..." or "As a result, I'd like to swap my existing 2 gang light switch in the lounge ...".
If it doesn't make sense like that, it doesn't make sense with "so".
But I'm happy with my lounge light switch? so should i be changing it?