Hmm, so many things!
Where are you located? What is your weather like? This whole week we are colder in sandhills of NC, than our daughter is in MT 35 miles from CN border. We also have humidity.
How is your "small" chicken coop built? Does it have enough ventilation for your 4 birds?
If you plan on using your coop bedding or run litter for composting, don't use DE. That will kill good bacteria as well as bugs. Chip drop was already mentioned. Since you don't your own trees, see who in your area does. Ask if you can pick up leaves. You may need to rake or provide bags. Saved feed bags work. Same w/ garden trimmings - a lot of gardeners are prepping beds for winter/coming spring(depending on where you are. Check to see if they used pesticides, if so, avoid that one.
Your local landfill may have & allow you to pick up wood chips. Some free, some nominal fee.
DLM in the run will usually do better w/ mixed natural materials. This provides different sizes - allowing pockets for water flowing through & aeration - causing the litter to "swallow" & digest the chicken poop leading to no flies or smell. If it starts to smell, you add more materials. You don't have to spread it, leave piled. Your chickens do the rest.
If you use hay & straw, spread out a bit in lawn & mow over it. Chops to different sizes - allowing above & it breaks down faster - no mold or slimeyness. If you use paper shreds, you may want to put 1/4" HWC on bottom of run to keep shred from blowing out. I've never had problems w/ this, but others have.
1 more thing - check drainage under your run. If water isn't actually going anywhere, it can contribute to smell & flies.
Include Rosemary & Sage in your plantings around coops.
Here is my post that I did in Gtaus's thread on paper shreds...
Post in thread 'Using Shredded Paper for Coop Litter - As Good As Wood Chips?'
https://www.backyardchickens.com/th...r-as-good-as-wood-chips.1503415/post-28208912