The perfect negative to lead up to the 's' is to have a rich selection of mid-tones, but with relatively flat but detailed highlights and shadows. This is on the principle that you can expand the tones by adding contrast, but it is difficult going in the other direction. Essentially you have to work within the dynamic range of the 's' device.

So a Pyro or staining developer works very well in this respect. My preference is for either 510 Pyro or DiXactol, and both can be used in pretty much the same way with a very similar dev time for all films at most speeds. The stain and working of the developer adds a tone to the highlights and shadows that stops them clipping. This can be made even better by using a semi-stand technique for developing where you only agitate every other minute, or longer. Some developers in this class are better than others with stand development, the two mentioned are very good, others can be prone to streaking.

But, it can be a case of 'swings and roundabouts' (meaning you can gain here and lose there) if you are using Pyro and staining developers with 35mm. Not all are as sharp as a 'normal' developer, and those that are sharp may give more grain. This isn't really a big a problem with medium and large format film, but can lead to disappointment with 35mm. You would have to test with your own film and developer combinations to find out if it will work. So with the two I have mentioned 510 Pyro seems OK to me for 35mm, if a little soft in detail, possibly favouring a slower film, while DiXactol is sharp but very grainy, and in small format not very nice grain (IMO).

Steve