I second the gelatin, but …
Until I was past 50, my nails were strong - not unbreakable, but quite durable, etc. Then I began to have problems, but the onset was so gradual that I didn’t really realize until one day it dawned on me that none of my nails was strong anymore, and several of them, including my right thumbnail, were subject to frequent vertical/lengthwise cracking/splitting.
First I tried some of the paint-on goop. AAMOF, I tried several different kinds, except for those which include some variant/derivative of formaldehyde. Formalin variants are mutagens! Given continuous use, they can be carcinogenic. It ain’t worth it, trust me.
I began using vitamin E hand lotions or creams every night. And it did help some. I strongly recommend this. I don’t think you can get a hand lotion/cream with both collagen and E, but if you can find one, use it! Otherwise, try both, and see which gives you better results. I am religious about the use of cream or lotion on my hands (with special attention to the more vulnerable nails), and it helps. But it’s not enough for me, and probably will not be enough for the OP - or anyone else who has this problem to a serious degree.
For any person who, like the OP subjects their hands to daily abuse, I recommend also getting a pair of white cotton gloves. After applying cream/lotion to your hands at bedtime, put on the gloves and sleep in them. Sterile plastic or rubber gloves would also work, except that it would probably make the user’s hands sweat, and might even induce sufficient discomfort to wake one up.
Some months after I began using the creams, something came floating up from the depths of memory. I recalled that when I was a teen, and girls were having trouble with their nails, they would buy Knox Gelatin (a pure, unflavored relative of Jello[sup]TM[/sup] made from bovine sources, and therefore illegal for those who keep kosher; dunno about hallal), dissolve it, and drink it. The ones who tried it swore by it. And I recalled having seen gelatin capsules in the vitamin & supplement aisles. So I started taking it (in addition to the nightly thorough creaming), and it did help … some.
About two years ago my pain doctor told me to start taking glucosamine (for my joints). Only a couple of months after I started that, I began to see a larger improvement in my nails. I don’t know if there is any reason why a person should not take glucosamine for this reason (AAMOF, I’d think that anyone who, for work or play, engages in strenuous physical activity would find it helpful to be taking this; there is medical evidence of its usefulness in rebuilding joint cartilage), so I’d recommend asking one’s family doctor whether there could be any harm in it. I really don’t think there is, but I do not know. The daily dosage I take is three 1000 mg capsules. Anyone who decides to try this should start out at a lower dosage, I think.
Another thing one might try is getting some of the stuff used to heal/strengthen horses’ hooves. The stuff I’ve got is Hoof Quencher[sup]TM[/sup]. Depending on one’s location, it might be necessary to go to a pet supply store, or find it online somewhere. But don’t apply it when you’re going to be washing your hands soon after. If you can’t find it elsewhere, try Vermont Country Store I think they still carry it - no time to check. <gasp>