Hello!
My routine before shaving:
1. Putting safety razor, blade and brush into hot water while I am showering.
2. Hot shower.
3. Assemble the blade onto the razor and fixing a good lather with my shaving brush.
4. Letting the cream stay on for about 1-2 minutes, before the shaving begins.
5. Shaving with the grain, never against it. First round done.
6. Rinse with hot water on my face and applying new shaving cream on my face, while doing this I leave my razor with the blade in the hot water.
7. Shaving with the grain once again and when everything is set and done, rinse with cold water on my face. Finally applying a aftershave.
My current setup:
Merkur 34C
Tabac Orginal Soap
Merkur Super Platinum, I tested about 8 brands and this gives me the least problems.
Edwin Jagger Shaving Brush
Nivea Men Sensitive After Shave Balm
Couple of thoughts ... why are you warming the blade and razor in hot water? I have to wonder if the heat of the blade isn't making things worse, because it seems like such an outlier. I've never heard of anyone doing that.
Here's what helped me, and I endured neck bumps and ingrown hairs for YEARS before switching to DE shaving. Like you, I STILL had problems when I switched to a DE. Here's what helped me.
1. ABSOLUTELY no pressure. NONE. If you think you're shaving without pressure, I'll challenge you to go even lighter. And make sure your angle is right.
2. Stop using Nivea Balm. I know a lot of guys use it without issue, but I've come to realize that I need an astringent routine AFTER my shave in order to assist in healing and facefeel. I used a balm for years and once I stopped, my neck bumps were gone.
3. Adopt an astringent post shave routine. Cool water rinse, followed by a splash of good quality witch hazel. I love Thayer's Medicated. Finally, an alcohol based aftershave splash. Consider something like Fine aftershaves or Clubman. I started using Clubman when I first switched to splashes over balms and had great success. Whatever you use, by and large, doesn't matter as long as it has some alcohol in it. I prefer the Fine stuff now, or Barrister and Mann aftershaves, because I enjoy their scents and my facefeel is better over Clubman.
4. Take a day off between shaves. Oh ... and ONLY one pass. That's really all you need.
You can experiment with other things ... in time I found out that my dad's old Ball End Tech Gillette gave me the absolute best shave of all the razors I tried, so now it's the one I reach for when I shave.
Good luck!