On top of what others have said, I will recommend resistance bands. Combined with a door anchor, they are an extremely cheap and versatile type of workout equip

On top of what others have said, I will recommend resistance bands. Combined with a door anchor, they are an extremely cheap and versatile type of workout equipment. It is surprising how much of a workout you can get with them. They're not a complete substitute for actual weights, but they are good for a home session. As a bonus, if you travel, you can easily stick them in a suitcase