Sorry to hear about your problems with heavy lifting. Re the pelvic floor exercises, I hear you. They are easy to forget or just skip, but then we begin to have pelvic floor problems again.
This may (probably will) sound strange to you, but think of what you do when exercising at the gym, or even when lifting in your job. We usually exercise against resistance. This also can apply to our pelvic floor exercises or Kegels. When I had to back off from doing very large number of Kegel exercises, I found that fewer exercises, but against resistance, provided greater improvement without causing chronic muscle fatigue.
By "resistance" I mean inserting a soft anal plug that the sphincter muscle can contract against during Kegel exercises.

I use enemas to control my bowel incontinence and purchase retention enema nozzles from silicone nozzles.com. I bought a soft and pliable anal plug from them to use during Kegel exercises. I only use the inserted soft anal plug for Kegels about twice a week. The rest of the time I do them the usual way, without resistance. The combination has worked for me.
Try starting a Kegel contraction immediately prior to lifting. That should help reduce the sagging of your pelvic floor.
Don't forget that you can do Kegel exercises while at work or just walking around. While there is no guarantee that will be completely adequate to your needs, they should help.
Good luck and let all of us know how things are going. Feel free to PM me.
--John