Yes, toppers and pillows can be DIY’d. Here is my pillow post, you will see that many of the pillows, I created myself. Many modeled after pillows I have purchased. I have purchased 100% cotton zippered inner liners and quilted pillow covers in both wool and cotton. I have acquired blonde horsehair from a source in Italy, wool batting from Sonoma Wool, latex noodles from CozyPure-Ebay and Amazon suppliers.
I generally prefer fills that are uniformly cut and consistently sized, rather than random shredded foam. Consistency in fill size makes the pillow more predictable in how it compresses and displaces under your head. It also makes it easier to fine-tune the feel when adding or removing fill.
That said, not all randomly shredded fills are bad. My Brooklyn Bedding shredded foam pillow is actually quite good. Although the pieces are not as uniform as I would prefer, and the foam quality is decent, so it doesn’t clump or shift too erratically.
DIY toppers are trickier. You’ll need a proper topper cover, which isn’t always easy to find. Standard duvet covers won’t hold loose fill in place, so you need something either quilted or segmented to prevent the fill from shifting over time. Tufting, baffling, or creating ribbed channels can help keep the fill evenly distributed, but they add to the complexity of the project. If you can not do this part yourself, it is kind of tough to get someone to do it, perhaps your local dry cleaner could sew the baffles or ribbed channels.
Even if you purchased a single piece of latex, you would need to buy a stretch cover to it. You are not likely to save much money buying a layer of latex and nice organic cotton stretch cover, opposed to buying a topper from someone like latex mattress factory or mattresstopper.com.
To make a noodle mattress topper, which is quite nice, sewing it would be a PIA.
Buying a layer of memory foam and cover is much the same as it would be for solid latex.
The main reason I crafted my own pillows was due to the fact if the loft on my pillow was as little as an inch and a half offer, my sleep suffered. I had to add fill to my cozypure baa-noodle. The Brooklyn Bedding was filled quite well. The cube filled latex pillow from European Sleep Works was good, but I had ordered extra fill just in case, but I did ask to over stuff the pillow when they created it for me. The Oxygen Pillow ESW created for me was calculated from the start and is great.
One of the more interesting creations was the Serta Memory foam pillows from Sams Club. 2 for 12.98. They sucked, but since they had zippers, I took about 50-60% of the fill from one pillow and overstuffed it in the other pillow and it was pretty good, although a bit lumpy. Most people would never know the difference. I bought a second set of the 2 for 12.98 and created a 2nd overstuffed pillow. The guests seem to like it. LOL, Basically for 2 over stuffed pillows, it was $26, the best bargain as I could not buy the fill for that price independently.