A thought;
From my one and only visit/experince with a specialist vibration control service provider - seems many rubber isolators come in a range of durometers.
Selecting a mounting isolator system, that has the option of using the same design/dimension isolator, in diffrent durometers, may be the way to go.
Example; https://hutchinsonai.com/wp-content/uploads/2020/05/Barry-Controls-2011-compressed.pdf Page 87, 22000 Mount Series
Note: Not suggesting that the 22000 series Barry Controls mount will suit your application, just demonstrating that some mounts will be available in a range that will allow you to select softer or harder isolators..
In my quest to control my engines movement, I have moved from Sonex supplied Barry Controls PN 22001-13 to 22001-14 - so far so good.
(See Barry Controls Specification Chart Page 92)