Home Based, Cycling Specific Workouts and Stretching - Resources Please?

Hi all,

I'd like to start doing a home based resistance training programme and stretching / flexibility routine.

I turn 50 later this year and figure that if I want to keep doing this great sport, I have to take better care of myself - right now I just ride my bike :) - I'm gonna address sleep, diet, some core strength and flexibility to compliment the riding.

I was a roadie, then a commuter, then a MTBer - for the last 6 years of been cycle touring and BikePacking - now I'm back on the MTB and ride to work each day......I'm a cyclist;)

I have an empty spare room and happy to get a Yoga Mat, Kettlebells, Swiss Ball, Stretchy Bands etc to kit it out - I suppose body weight is a good starting point??

Can any of you fine folk point me in the direction of some online resources for cycling specific workouts with progression and a suite of stretches that I can do from pics or diagrams (I know the basic ones)
Ideally a full body workout 3-4 times per week. Happy to follow along on a YT clip from the iPad...

I've noticed when getting off the Touring /Bikepacking Bikes and back on the MTB, my body is having to work much harder and I feel a lack of strength and control......does that make sense?

Thanks in advance if you're able to help me out!