No Stupid Questions

Just search for "kneeling pad" or "gardening knee pad" and you'll find a bunch of pretty durable options for around $10. Or, hell, just get a pair of skateboarding knee pads. You might not be the pinnacle of fashion, but your knees will be well protected.

Google "Knee sleeves" literally designed for the purpose.

Rubber mat, like those rubber toy mats which can interlock. Or a workers knee pad, which isn't rubber as I recall, but another, tubed, soft plastic to coushion the knees. Pic related.

I use a large folded microfiber towel as knee support in pilates. It’s not as spongy as a normal towel but soft and supportive enough for those exercises that put a lot of stress on my knees or tailbone.

Depends on the type of yoga mat! Some are very thick, some are very thin. Sounds like you got one of the thinner ones. You couldn't possibly fold one the thick ones, it would open up on its own without a weight on it whereas the thin ones can stay as you leave them.

A kneepad is another option as many said already.

You also have mats for camping, my parents had a couple of these and they would lay them under the sleeping bags precisely to avoid feeling all the debris on the ground.

They make thick pads for gyms that are designed for exercises where your knee is on the ground. I used them for a while

https://www.bunnings.com.au/cyclone-knee-pads_p0122526

Gardening knee pads. Designed for spending hours kneeing in the dirt, and are flexible

Hardware stores might have cheap gel knee pads ($10 -> $40 for fancier ones)

There's also these kneeling mats / pads

G-Form mountain bike pads would work.

You want the X3, not the rugged.

https://g-form.com/collections/bike/products/knee-pads-mountain-bike-prox3-alt

Look for a knee pad for gardening. Go to the gardening section of your local home improvement store. They're just big enough to kneel on. If that's still too big, maybe look for an inflatable camp pillow or camping cushion of some sort.

Swimming kickboard/flutter board?

Perhaps a soft kneepad that you wear would work for you

It will get easier the more you practice and your bones will get stronger. If I'm uncomfortable I just change positions.

you could get a cheap foam thermal mat and cut out the size you need. beware though, as it will roll up by itself when too small.

I just use my pillow or maybe a folded towel if I have to get on my knees for an extended period.

Hover your knee off the ground when you are in the all-fours helps. Like don't put your whole weight on it. Do poses that don't put as much weight on your knees. Look for better ground to practice, grassy areas.

When I yoga outside, it's the last suggestion I use the most. My knees are also sensitive, and finding a flat surface, then using my usual sorta thick yoga mat works well.

I agree on the knee pad, but most of these seem a bit overkill. I'd go with a sleeve like this or a more lightweight knee pad like this.

In my homegym I have an AbMat foam pad which I also use as a knee pad. And while I think the thick foam would work outdoors on tougher terrain, it would not meet your criteria to fit in a backpack.

My other suggestion would be a scrap piece of horse stall mat, which are nearly solid rubber sheets commonly employed for homegym floors. This is what I use when working in my yard, for tasks requiring a lot of kneeling. Such a piece -- while heavy -- could be cut to whatever size you need, using a sharp knife or a jigsaw.