Speaker outriggers

@jmphotography ,
I take it your floor isn't level, hence the need to add a washer, is that correct?
If so, I would look at something at Herbie's, as it should be in your budget.
https://herbiesaudiolab.com/collections/loudspeaker-rack-decoupling-and-isolation
Actually, I would call them to get the best information on what you should get.

Though I will second Townshend Audio products, they are very effective, but very expensive. I use them on my components to great effect.
Bob

@jmphotography ,
There seems to be two  schools of thought when it comes to isolating speakers.
One, like millercarbon aludes to uses springs to isolate speaker vibration.
(And, I do use the Townshend products under my equipment, though not under my speakers).
The other is one that Vandersteen uses, which entails using a thick piece of marble on which the speaker sits using spikes that are set on a special felt that reduces movement and anchors the speaker to the marble base.

Being a cheapskate, I opted for 3 inch butcherblock with some sorbothane pucks under them. It works well for me.
YMMV.
Bob