I just use Gm(maj7). It’s not so much an alteration but an addition in this case, but with Gm7(maj7) the first 7 seems unnecessary unless you truly mean there’s both a lowered 7th and major 7th in there.
I hate G-#7 as I don’t think that - should ever be used to mean minor, as that’s just a relic from lazy hand copyists. I actually really like the nomenclature system that uses + and - for alterations though! If you only use + and - for alterations then there’s generally no need for parentheses as the distinction between root accidentals and alterations is clear and there can’t be any confusion. Jazz at Lincoln Center and David Berger used that system for years for example. (Dave switched up nomenclature systems when he started using Sibelius and I have no idea what J@LC is up to anymore.) Without parentheses you can save on horizontal space which can be important with composers that use a lot of chord symbols with a lot of alterations. (I was Slide Hampton’s copyist for years, and this was an issue with horizontal spacing in his music for example.)
The problem with the ± system, is that it doesn’t really work for the chord we’re discussing here as something like Gm9+7 or Bbdim+7 just doesn’t feel correct to me. I assume most people will still interpret them correctly, but something about it bugs me as it’s not really a #7. As long as - can never mean minor, all the distinctions between Bb6, B-6, and B(b6), are clear, and you can eliminate the parentheses with B-6 or C#7+9 using that system.
I was just at a rehearsal Tuesday where the composer had a Ab6 chord where both the flat and 6 were superscripted and we had to stop and ask if she meant an Ab chord with a 6th or an A chord with a flat 6th. (The kerning between the A and the flat was also particularly poor making it look even more like the flat belonged to the 6 rather than the root.) Adopting a clear nomenclature system that eliminates any possible ambiguities like this is pretty important to me.