I am thinking of making my next Mt bike, full suspension. Right ride hard tail.

I do all my mt bike rides as X country.

just recently did an endurance mtb event of 100 miles. Which was ridden lots on trails.

Now i found that my lower back was in horrible pain the whole time on the trail, that were notoriously bumpy. I saw that the other rider with their full suspension seem to ride those bumpy back breaking trail way more smoothly with the full suspension.

Now I ask would i find many benefits to a full suspension?

Would that rear suspension help to take off some of the pressure off my back when riding such bumpy trails.?

i will admit i do keep my tires at high PsI as i hit getting flats.

I like to hear all your suggestions? and advice on this
before i go out and spend $3000 or more on a full suspension?