Looking for a good everyday carry pocket knife as a tool and as a self-defense weapon.

Hello! The question is literally the title. I'm looking for a good everyday knife. Here is some context and extra info:

I live in a place where I can carry an open carry knife of any kind, and a concealed carry knife, with the limit of it being a foldable pocket knife under 4". 

I currently have a basic 3.25" folder I've used for years and years, but I've started looking into better options, as it is not a super high-quality knife lol (quite literally like 10 bucks). I've also had to replace various parts best I can, over the years, so it's kind of mismatched now.

I will also keep whatever knife I get for as long as I possibly can, and put some serious wear into it.

Current Knife:

https://www.walmart.com/ip/Ozark-Trail-3-25-Inch-Folding-Knife/19718065

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Concealed / Open Carry:

Since the laws about whether or not just having the clip of a knife outside of a pocket showing is considered open or concealed carry are kinda unclear here, and I sometimes wear clothes that cover the pocket I put my knife in, I want to stick with something I can legally conceal carry.Looking for a good everyday carry pocket knife as a tool and as a self-defense weapon.

For everyday use:

I use it for opening boxes, cutting rope and stuff, minor wood whittling, and things like that. 

I use the absolute shit out of my knife, and basically always have it on me.

For self-defense:

Yes, yes, I know. Knives are not a good option for self-defense, and I should use mace/pepper spray, use a gun, or run, etc., etc. I get it. BUT! I already carry mace/pepper spray, I like having multiple options for different circumstances, and I can't carry a gun here at my age. Also, if I could run and get away in a dangerous situation, I would, but sometimes that is not an option. So, this is for a scenario where I HAVE to use my knife over anything else. I also have fairly decent self-defense skills and knife attack/defense skills. (Please don't barrage the replies with that whole spiel 🙏.)

But I am not particularly big or tall, I'm a woman, live in a big city, and I work in a place where I periodically deal with some fairly volatile people, so having another last-ditch safety measure is comforting.

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Ideal: 

The majority of these, I'm flexible on

– Not insanely expensive because I'm a broke Uni student. Like max $120-ish (≈100€) probably, unless that is really unreasonably low for some reason, and I won't be able to find anything in that price range somehow. (I'm not really sure how expensive decent knives are)

– I prefer longer blades, so like 3 to 4 inches (≈7.5-10 cm) would be ideal. (But I am significantly more interested in a 3½-4 inch)

– My current knife is fairly sturdy and a comfortable hold (because it is fairly wide in the direction of the blade [like the narrower part(?)]), which I appreciate.

– Locking blade is basically a must! I wayyy prefer a locking knife.

– I've basically only had frame lock knives, because I really like them, but I'm willing to try something new. :]

– Blade type(?): I have only ever had blades with no serrated edge, which makes them super easy to sharpen (which I have to do often because I put some serious wear on mine and it's old), but that doesn't mean I'm against them, as they can be very practical. But I was under the impression that sharpening a serrated blade is difficult (maybe I'm wrong?) But I'm definitely willing to give it a go and do some more research on sharpening! 

– Being able to take it apart, to clean and stuff would be great, but I can live without that option. (and for ease of part replacements if necessary)

– A sturdy/good pocket clip is definitely appreciated!

– Having a marlinspike (love these!), seat belt cutter, window breaker, bottle opener, and other practical stuff like that is lovely, but not a requirement.

– Not horrible looking… my current one has like nice wood accents, and just is overall nice and sturdy looking, which I appreciate.

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I don't know, maybe my current knife is just the best I'll be able to get for what I am looking for, but I thought I would ask the professionals of Reddit :]

Sorry for the lengthy list of requirements and whatnot, but I would really appreciate any help! Thank y'all and have a good day!