TheSword
Legend
It is really tempting, similar to the Epic 6 approach mentioned earlier. My concern is that by limiting the level you take some of the fun out of the play. It preserves the feel of WFRP the best I agree at the cost of stagnation. As someone who is 2/3 of the way through Ghosts of Tsushima and has all the skills I know how demotivating that is. Slower progression and freezing HP might work.This is because D&D is designed for adventures where you routinely use violence to solve your problems. In fact, combat is designed to be fun and exciting - in D&D, combat is a reward.
WFRP, on the other hand, is designed from the stand-point where combat results from failure to avoid combat. Choose the violent path too often, and the RNG gods will send you to an early grave. It is a completely different philosophy.
Not sure if this really fits the "plus" tag of the thread, but the fundamental aspect of WFRP combat is that you can only ever soak a single solid hit before you risk taking criticals.
That is, weapons deal pretty much the same amount of damage in WFRP as low-level D&D. Yet characters never gain more than maybe 20 hit points or so (depending on edition). So pretty much everybody can escape grievous harm from a sword... once. That's it.
Sure, you can play WFRP in a slightly more heroic and mass combat:y way by wearing heavy armor, and you can go over the top by adding Dwarf Toughness to that, but many groups prefer playing "civilians" that settle for conquistador armor (breastplate over leather, plus metal helmet) tops, and you never become fundamentally impervious to the attacks of regular orcs and goblins, bandits and such.
The point is: adventures are written with this in mind. Add D&D fighters and wizards, and much of the point is lost. You really need to be fully aware these adventures are written without the standard D&D expectation ("if we encounter a monster and aren't given heavy clues to run, we can defeat it") in mind.
I guess the simplest way to model this is to restrict play to only the lowest five levels or so. (This gives you only a single level of true superiority to low-level threats. And at first level, D&D heroes are arguably even more fragile than WFRP heroes!)
More generally, about the only way to represent WFRP combat in D&D is to skip getting extra hit point from levels. Or rather, make the Hit Die a "1" for every character. That is, wizards and warriors alike gain 1 point per level, plus your CON bonus. (The expectation is that physically fit young men and women are those picking up swords and clubs, while less impressive specimens resort to their brains, their agility or their charisma That is, warriors gain more hit points than wizards, thieves and troubadours not because they have a larger hit die, but simply because they tend to have a higher Constitution!)
I'm not sure this really is constructive enough for your plus tag, so let's end on a positive note: I'm sure you can have great fun playing D&D in the Old World, but let's not pretend it doesn't make for a fundamentally different and decidedly more heroic game experience
Maybe that fragility will just have to be sacrificed and the random chance of having your arm chopped off when down to 0 hp is the half-measure. I think @BookTenTiger ’s escalating combat where when things get bloody all damage is doubled could functionally be the same as reducing hp.
