Bodyweight is king my friend! Circuit training is intense and is great for keeping the heart rate high through and burning more calories.
Great you’ve found something that works for you. Push ups: diamond, clapping (explosive), incline, decline, wide there’s literally so many. Way harder ones than those too but they’ll prolly do for now. Squats it’s a bit harder without weight, you could try isomeric holds.
One way to sure progressively overload is to add weight and you can do this by buying a weight vest. I’ve got one and I love it. These are often fully adjustable weight wise and even adding a small amount of weight makes movements more challenging.
I’ve got this one: Gravity Fitness 20kg Weighted Vest - Fully adjustable. Calisthenics, Crossfit, Strength Training, home and commercial use. https://www.amazon.co.uk/dp/B07TVNTBZ3/ref=cm_sw_r_cp_api_glt_fabc_0VGRR137458PGGD8E5SM.
I know it’s £100 but IMO it’s all you need equipment wise.
I think some sort of pulling exercise would be good to add to your programme. Is this possible? Do you have access to a pull up bar?