Modest female workwear is probably hard to come by, but you can find stuff on a site like Etsy. Think something like an overall-style dress. Front pouch with pockets, duck canvas or denim is hard wearing if you're going to be doing labor intensive work. 100% linen would be ideal but I doubt you'll find a linen workwear dress. Examples:

https://www.etsy.com/listing/1765791253/denim-overall-dress-women-overall-dress

https://www.etsy.com/listing/4309047254/vtg-workwear-pinafore-cotton-jeans-dress

Roper boots are more suited for mucking around than anything with laces, as the only opening for dirt/debris to get in is at the top. Rubber boots (or "wellys", as you non-Americans say) for when it's really wet out

Can I ask what kind of work you would be doing? Is it with animals? Or is it dealing with crops or gardening. Or both? 

I live on a farm and do daily chores. For almost everything I do I wear a heavy cotton or denim skirt. It’s sufficient for gardening, milking goats, climbing in and out of equipment, etc. Ankle length is no problem while doing those things. Don’t wear skirts with flimsy material because it gets caught on eeeeeeverything. 
Sun hat, absolutely. 

The only time I absolutely will not wear ankle length is if we are sorting livestock and catching them to castrate or tag. Sometimes this leads to angry animals and if I need to run, long skirts are only going to slow me down. For safety reasons I wear the same type of material but the length is about 6 or 7 inches inches below my knees with cotton leggings or bicycle shorts underneath.

Muck boots for muddy conditions, a nice strong boot for every day wear. 

In the olden days we all wore split skirts.  Some call them coulots or riding skirts. made from denim.
They are great for almost any kind of farm work, on ladders picking fruit, mucking stalls, milking, and of course riding albeit today it would be on a tractor not a horse.

Here's a pattern

RH1024 — Quick Print 1910s Ladies' Cycling Split Skirt Pattern - Etsy Canada

Make sure you add deep pockets
Also get high rubber boots and have the skirt come at least three inches over the top of the boot otherwise it becomes annoying.

Thanks, I used to quite like split skirt, yet some argue it was feminist and a pioneer for the upcoming trend of women wearing trousers. I dont know what to think about that 

Thanks, I used to quite like split skirt, yet some argue it was feminist and a pioneer for the upcoming trend of women wearing trousers. I dont know what to think about that

Wear a split skirt under a regular skirt or dress as a slip. Be sure the outer garment is wide enough, pleated or closely gathered at the waist. 

Wear a split skirt under a regular skirt or dress as a slip. Be sure the outer garment is wide enough, pleated or closely gathered at the waist.

This is basically what I wear and used to do for the farm:  loose cotton pants or homemade ankle length cotton drawers with cotton/denim dress or skirt (which was gathered at waist or had an A-line to have plenty of flow) over top.  We did everything on my parent's farm from picking strawberries, scooping manure, making trails, riding horses etc.  We used to joke that there wasn't much you couldn't do in a dress if you added the proper loose pants/cotton drawers underneath.  😅