I think the big elephant in the room is...
Knifes where never an big thing in warfare.
Pointy sticks (spears) where pretty much the choice aside slings, then bows, crossbows, then any form of missile weapons.
Bajonets are more an psychological thing (yes they where used as weapon but the major point was not for killing, fatalities due to bajonet use where never the big thing, changing the tide of battle, a crowd of howling insanes charging with them though...it was more about psychological warfare, game of chicken).
If someone attacks me with an knife any sort of stick with enough weight is already an superior weapon. (real world not against the super triple worldmaster in knife combat situation)
Knifes are tools 99% of the time, so that is where i would focus on, not on sticking them into people, for that an good sized screwdriver already works quite well (and at the fraction of the cost, plus legal next to everywhere)
So well, the knife i carry is sturdy, holds an edge and is someway easy to sharpen to cut things, pry open things, serve as screwdriver, step on while sticking somewhere, lever, hammer things down, and cheap enough to be easy to replace.
It is an tool, not an weapon.
If i had to choose an weapon for close combat I would go for something that has an point (slashing modern fabrics, especially the type used by people who are in the buiseness of fighting is notoriously hard to cut.) and there the mentioned screwdriver with some "modding" comes into the game.
IF one wants to use an knife for close combat I think serious training is THE thing, knifes are pretty specialised.
Actual combat knives tend to be double edged and very pointy for an reason, the "survival" knives do not have that, they are shaped like "tool" knives, (or they would be daggers...)
Ancient knives used in combat where in the region of 15 to 30 inches and double edged. And never thought of as the first, second or third choice.
It helps to know some history of people who had to deal with close quarter combat as a matter of "normal" life.
If we talk swords (super knifes) then again, anyone who had an quarter staff and was trained in its use was already an major headache for the sword user.
That tells us that even swords where more a thing of convience and status, but not an first choice even for face to face exchange of arguments of rather physical nature.
Knights (and samurai) who are kinda all about swords did not use them in combat as long they had pointy sticks, heavy sticks, sticks with strings attached to shoot pointy sticks with avaiable, they used there sword as last resort (in actual combat)
Roman soldier would come to mind as the soldiers who used swords (or oversized knives) as primary weapon and that was under very specialised tactical conditions (and pointy and double edged, again)
Todays "combat" and "tactial" knives are tool shaped knives. not "weapon shaped" knives.
Close combat is about what one can grab and use, having an knife just for that reason is not really helpfull because it implies that the situation allows to employ it in an usefull fashion.
If one is really and serious concerned about close combat i would recomment street fighting training, (so called dirty tricks) where one learns not to think about what weapon to carry and how to use it but about how to use whatever is at hand, every normal room in todays life contains a lot of things more lethal than an normal knife (the "tactical" or "survival" shaped ones).
Hell, steelcapped boots or any equivalent to the knee can end an knife fight very quick and painfull. Do not focus on knives (as weapon) is my opinion, especially not the so called tactical or combat shaped ones offered, what you talk about here is dagger, two edges, pointy and about double the length of an k-bar.
