Just to add, you can do strength training just fine without a gym membership, and exercise every muscle group. There is an endless sea of web content to teach weightless workouts.

Simple examples..

Back: pullups. Too easy? Use one arm.

Chest: pushups. Too easy? Vary your arms position, or just use one arm.

Legs: squats. Too easy? Use one leg.

Abs: sit ups. Too easy? Hold something heavy against your chest. Too easy? Hold something heavier.

It's not rocket science :) Motivation is the only ingredient you need for all the exercise you can tolerate.