Great question. I'd be interested in some ideas too. I'm especially interested in finding some organic material that has not been doused in chemical treatments. Something that would wear well, like jean material, and cottons for tops. And patterns to sew.

I can't see making gloves, though because I like the Nitrile material that fits so comfortably you feel you don't even have gloves on.

I haven't had luck with knee pads, they keep slipping out of position, so I use a kneeling pad.

A coverall, like Farmer Greenjeans with places to put tools etc, maybe, in a cute garden pattern.

Jersey knit cotton tops. TShirts with short sleeves but 'long' short sleeves.

I'm so glad I'm not the only one curious about this.

As far as fabrics go.. I know what you mean. A lot of regular fabrics at the regular stores are very... processed.

I know from costuming experience that plain untreated muslin is great for making loose fitting shirts and pants. I use this for undergarments for re-enactment garb, which can sometimes be very heavy, warm, and constricting. And the stuff comes in widths up to 108 inches pretty standard in local craft/fabric stores.
I've had luck with some heavier and less chemical-ish fabrics from fabric warehouses. The tucked away places that buy all sorts of random stuff- and you can sometimes find oooold fabric thats great for a good price.
Also sometimes at the thrift stores one can find large chunks of fabric in the form of bedding, tablecloths, or drapery that can suit.

I have really small hands, so I often look in the kids section for gardening gloves. For heavier ones like leather. The blue gloves in small are still a bit big on me, but I use them a lot because I love them.

I've had terrible luck with knee pads too and use kneeler boards. But if the right pattern existed for a good set of knee pads..

For the jersey tops, try sleepwear or athletic wear patterns. Like multi-piece patterns of top, pants, and robe or something. The Tshirt tops usually call for more giving material like jersey.

I think I might have access to some adult one piece pantsuit kinds of patterns soon, mostly vintage numbers. I'm moving my mom and sister in next month and sis has all sorts of crazy stuff. Random old patterns that might be good for coveralls of various needs.

I also do a lot of sewing,but I don't use that time for sewing gardening clothes.

I wear cotton knit pants,and cotton or cotton knit shirts,socks that I tuck my pant legs down into,and long sleeve denim shirts or nurses scrub jacket with the knitted cuffs.I also wear big floppy hats or a baseball hat,and the nitrile type gloves.

I won't win any fashion awards,but I'm comfy,bugs can't get up my pant legs or my sleeves,and I don't have to worry about ruining any clothes,because there are more where those came from.Oh and everything has pockets,that's a must!
Kathi

A "cute" pattern for strolling in the garden. I don't think it would hold up to real gardening chores though.

I just came across this link

Here is a link that might be useful: homemade beekeeping jacket

By far, my most useful and utilized gardening garments are my heavy duty aprons. Both are sturdy, full of pockets, not so long that I can't readily get on my knees, strong straps around the neck and waist.