If you are doing professional work, go for the DSLR, it won't be much heaver or bigger than a proper mirrorless with a lens on it. In my opinion, if you can't fit it in your pocket, it's the same thing as a DSLR.
I've considered switching from my full frame Nikon D610 to a Sony A7S for a while. Mainly because of the sick ISO performance and because I'm kind of sick of the tiny auto focus field of the D610. But I know I will regret it, lenses and basically everything is more expensive in that game and besides the ISO performance, there isn't much gain in there for me.
For portability, I recently bought a Canon G7X Mark II, it's a great little camera as long as you keep the ISO under 800. The 24-100mm equivalent lens is great, it basically works for everything. It is totally the go to "Vacation camera" for me, although sometimes I regret not having my D610 to take extra sharp pics of some other stuff.
If I had a ton of money I'd get a Leica M9, its decently sized, manual, physical controls (this bugs me big time on the G7X) and the optics are great. But yeah, I'd have to sell my car AND one kidney for one of those.