No idea

Sokolov will soon be publishing a Samisch Nimzo-Indian repertoire for White on Chessable.

Hello, 

my first advice is to stick to the Nimzo-Indian. It is such a rich opening! But very demanding - Black plays on White's home court! 

Although I would change some lines: 
1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.Qc2 d6!? 
This must be better for White because of the bishops, but it is a frequent choice, if a stronger black player wants to create winning chances. 
Most striking example is Radjabov-Carlsen in the candidates (must win for Carlsen and he was successful). Use a database to study some games of players who use it regularly. It is related to the Bogo, but preparation will be of much help. Black must be flexible. 

                                          4.Qc2 d5 
(5.cxd5 Qxd5!? and 5.a3 Bxc3 6.Qxc3 0-0 7.Bg5 h6!? )
gets excellent coverage by Roiz and is a good alternative: 
(Grandmaster Repertoire The Nimzo-Indian Defence) 

                                          4.e3 

I strongly recommend 
Sokolov: The Strategic Nimzo-Indian. 
Sokolov covers all lines of 4.e3 from Black's and White's view. 
(But he does not cover the transpositions to the Saemisch!)
At last the new book costs only 3 Euro - a real gem. 

You said you don't want d5-systems anymore. 
Then maybe this is interesting: 
4. e3 c5 5.Nge2 b6 (or the more solid 5...Ne4); 
4. e3 c5 5.Bd3 Nc6 6.Nf3 Bxc3 7.bxc3 d6 - the Huebner; 
...                         6.Ne2 cxd4 6.exd4 d5. 
Recently Demuth has done a video series at chess24 about Nimzo/Bogo, 
where he has covered the Huebner with the 4...c5 move-order. 

4.e3 d5!? is another option 
with a likely transposition to the Ragozin with an early e3. This avoids a few boring lines 
which are chosen frequently by White after 4...0-0 + 5...d5
Independent lines after 4...d5 are 
5.Ne2 dxc4!? 6.a3 Ba5; 
5.Bd3 e5! 
5.a3 Bxc3+ 6.bxc3 c6!? 
Have a look at 
Richard Pert: Playing the Ragozin. 
Chapter 14 is about the e3-Ragozin, 
in chapter 16 you find the independent lines. 
(Richard Pert also covers 1.d4 d5 2.c4 e6 Nc3 Bb4!?   
Pert gave a complete repertoire against 
1.d4 d5 2.c4 and 1...d5 2. Nf3 Nf6 3.c4) 

4.e3 0-0 is the mainline: 
5.Ne2 c6 is recommended by Gustafson at chess24. 
It could still have some surprise value. 
5.Bd3 c5 (but aiming for the classical d5-c5 setup) is also recommended by Gustafson at chess24. 

If you are interested in 4...b6 of the Nimzo systems, then have a look at 
modern-chess.com 
Marin has a  Nimzo-repertoire with b6 against almost everything. 
The preview of modern-chess.com is very fair. 
You are able to find out what they cover and what they don't cover before you buy a database. 

And Hammer will publish a Nimzo-repertoire at chessable soon. 
I cannot get enough of the Nimzo 

Since when the Grünfeld gives an advantage to White? The opening is well respected at all level even for 28XX or supercomputers. I play it at 22xx fide level since almost by beginning, with good results but you need to work and to feel the opening. The most important for any openings: you have to like the resulting positions. As Rowson said in his masterpiece book on the Grünfeld: if you are afraid of a passed d pawn, don't play the Grünfeld

Other ideas for Black: Czech Benoni (less sound but not much work to do), Semi-Slav (perfectly sound but sharp and lot of work), Benko Gambit: positionnaly sound and playable under 27XX).