Hump jumpers - they're useful but you don't need to buy one.
For holding a needle, you can make a little pad of fabric, stick the needle point into it and then use that to hold the needle in place whilst you tighten the clamp.
As DF mentioned, folded beer mats (or any other folded paper, card or fabric ) will do the job
Fabrics are different thickness, so are seams and hems. The plastic hump jumpers are great for thicker stuff but for thinner things, sometimes just using a pad of the same fabric folded to the same thickness works well.
What you're trying to do is keep the fabric feed consistent. You have to help the feed dogs to keep doing their job by ensuring the fabric is always pressed against the dogs which means you have to keep the foot level, both front to back and side to side.
(It's the same issue that affects button hole feet attachments - gotta keep the foot level or at least pressing the fabric onto the feed dogs evenly the whole time)
For some jobs like edge stitching and top stitching, there are compensating feet for industrials. We can achieve the same things at home by using folded strips of material to prevent a wide foot from tipping side to side.
For edge stitching shirt collars, button bands etc. then I often use an old collar or the sample made to test the interfacing/fabric marriage to keep the foot level if I'm using a wide foot machine.