The traditional "7 Minute Workout" includes two exercises that require a chair or other elevated surface, the ones mentioned above in the title. Due to an unfortunate incident involving a guest who twisted too quickly in their chair and shattered the back (freak accident, I suspect), my wife has banned use of the chairs in the house for exercise. Until I acquire a secondhand chair from Goodwill, what are some good substitute exercises? It would need to be something I can do at high-intensity for 30 seconds. The two exercises are listed as "Whole body" and "Upper body" respectively for the body parts worked in the original list.
I can recommend diamond push-ups or bodyweight tricep extensions both of them in combination with doing wide grip push ups where you go close to the ground and swing from the left to the right without pushing yourself up.
If you’ve got steps in your house/apartment, you can duplicate those exercises easily. In fact, stairs can be used for a variety of exercises. For starters, try Stair Tricep Dips with Triceps press on the stairs. You can substitute step ups on the stairs for your leg work. Additionally, if you can get a hold of an exercise ball, or, aerobic step, those make good substitutes for chairs also.