But my diet is awful and I find it tough to motivate myself to exercise
You've no chance if you don't address this honestly and directly.
I have a big appetite and that's that. So I shop seperately for myself, buying healthiler ingredients for quick meals and snacks. I don't let myself go hungry.
I love the idea of going for walks, but I don't do it. I have weights at home, and use them daily. I have a mini trampoline, good for bouncing, walking on, doing step-ups on. I put music on or watch TV whilst I'm on it. I keep them in the living room which is fine as I don't have visitors - if they're tucked away in a cupboard or another room, then I won't use them.
My motivation is rubbish so, I get how you feel. If I knew I wouldn't gain weight and ruin my health, I'd happily much on savoury snacks and sit on my backside for ages. But that's not the case so in terms of paying attention to what I eat, and exercise levels, it's got to be done.
I suppose I'm a lazy exerciser compared to some but my fitness levels and BMI are fine. I will never take things to the extreme, too joyless for me.
You could download NHS weight loss apps, good for a bit of motivation. & it's nice exercising at home, no-one to see you🙂 God knows what I look like when I'm jumping around.
(DSis gained hormone weight after failed IVF, it's a bugger to lose but she has. Not as low as her previous weight but she's toned and fit)
Good luck