If you want to get one pair of boots for the rest of your life get something with an all-leather upper and goodyear welts. All leather upper means real top grain leather, so no plastic, no nylon, nothing made by glueing leather dust or other waste material together. Barring mechanical damage from scratches, cuts, or scuffs good quality leather will last years and can last decades. If it's kept clean and oiled it doesn't decay in the same way the plastic materials used in modern footwear does.

When looking at leather shoes, look at the grain of the leather. The top side, facing out, should be smooth but the organic pattern - wrinkles and variation, of the animal hide should be visible on close examination. If it's slick and plasticky it's fake or manufactured leather and will decay. The specific industry terms for the material you want is top grain or full grain leather. Anything else is either plastic or something made from leather dust and glue and will fall apart. Don't get anything with suede. Suede is made by shaving off the actual outer skin of the hid and gives up much of the leather's strength and integrity. Top grain or full grain leather.

To maintain your boots - plastics are made flexible and supple by chemicals called plasticizers. Plasticizers slowly leach out of plastices resulting in them becoming weaker and increasingly brittle over time. With leather the fibers inside the hide are kept supply and flexible by applying oil. The tanning process and contents of leather conditioning polishes and oils prevent the leather from rotting. As a result leather's lifespan is limited mainly by mechanical damage - cutting or abrasion from the environment or the fibers actually breaking down from years and years of use. Keeping your boots oiled and polished will prevent most forms of decay - rot and dry rot - from setting in.

Do - use a leather conditioning oil. Neatsfoot straight from the bottle works in a pinch but there are lots of leather conditioners out there.

Do - polish your boots regularly. You can find instructions online but the basic idea is 1.) Use a warm wrung-out rag and a soft brush to remove dirt and crud. 2.) Use a rag to generously apply polish to all leather surfaces (i use Kiwi). 3.) Use a rag to rub in all that polish 4.) Buff with a soft brush until it shines. You don't need to be able to shave with it, but that shiny surface is a flat layer of waxes and oils that produces a mechanical barrier against water and chemicals getting in to your boots

Do - dry your boots out after use. Water is a primary source of damage. Dry your boots thoroughly then apply a light coat of oil.

Don't - use silicon based waterproofing sprays. They work very well, but they can also prevent oil from getting to the leather which can lead to breakdown of the leather upper over time.

A goodyear welt is the manner in which the sole is attached to the boot. A goodyear welt allows the sole to be removed and replaced when needed. This extends the life of your footwear indefinitely. As long as the uppers remain intact you can continue replacing the soles. I'm a fan of vibram outsoles, personally.

The last set I had were built to wwii spec with leather insoles. I put the foam insoles you find at pharmacies in them and swapped as needed.

Consider investing (like 5$) in a leather hand stitching awl

This thing - https://www.buckleguy.com/413-automatic-awl/

Probably don't pay 32$ for it but make sure you get good waxed thread. Learn how to use it and you can make repairs in most leather goods. Most stitching awls have needle storage in the handle so you can throw it in a backpack and make repairs in the field.

All leather upper, good year welt, make sure you get fitted by a professional. It'll cost hundreds of dollars, but the Sam Vimes Boots Theory of Economics is real and specifically applies to boots. This concludes Frank's semi-annual "How to die in the same boots your great great grandpappy invaded Normandy with" lecture.

Note: if you're unwilling to buy leather then consider used leather boots. Again - if they're kept in good condition they'll endure indefinitely and you can get boots that are already decades old, slap new soles on them, and be gtg.

Note: leather work boots will often give out in the toe first. This is especially true for steel capped boots as the leather will get pinched between the steel cap and whatever you just kicked causing damage. There are various toe repair products that can be used to prolong the life of the boot, usually in the form of a plastic goop that is applied to the toe and dries in to a tough flexible shell.

Additional note: ideally everything in your boots are held in place by stitching (which can be replaced if needed) and not glue. If you do see part of your shoes, leather or otherwise, coming apart where they were glued then you can use a product called "shoe goo" to repair them. It's a flexible waterproof adhesive designed for footwear. Follow the instructions and make sure to apply plenty of pressure to the parts being glued togetrher.