Core/Strength Ideas
Modify these workouts as needed- they can be intense, but will improve your fitness. Emphasize correct form over more reps.
This website explains the importance of core and provides 22 ideas with video/pictures:
https://www.menshealth.com/uk/fitness/a34037742/best-core-exercises/
This is a leg workout that can be done without dumbbells:
https://www.menshealth.com/uk/workouts/a60536393/30-min-dumbbell-leg-workout/
This has 31 bodyweight exercises. You can have days strictly for upper/lower body, or you can do a full body workout:
https://www.menshealth.com/uk/building-muscle/a756325/10-best-bodyweight-exercises-for-men/
This focuses on a few movements. Instead of doing the reps they say, you can go time based or pick a certain rep/set scheme:
https://www.menshealth.com/uk/building-muscle/a45480605/prison-workout/
This explians a HIIT workout, where the concept is quick reps as fast as you can and short rest periods. You could pick 2 exercises (ex. squat and pushups) and alternate those for 20 seconds work, 10 seconds rest for a designated amount of time.
https://steelsupplements.com/blogs/steel-blog/12-best-hiit-exercises-that-require-no-equipment
This has several different HIIT workouts:
https://tiffxdan.com/hiit-no-equipment/
Cross Train and Stretch
Explosive Drills
Lower leg