In my personal opinion, if you're trying to be sexy or whatever (my assumption for femboys), clothes that fit are better than oversized clothes. Oversized clothes generally are going to hide your figure. If there are aspects of your body you don't like you can find ways to hide them and highlight the parts you like, but that usually doesn't include becoming a human tent.
This of course assumes you are wearing clothes at all, why bother when you can just take nudes. (Again assuming this is mostly for pictures online for attention since that's most of the femboy stuff I see, not everyday styling. I don't have much advice on being a femboy 24/7, since boys/guys wearing that sort of thing in public isn't generally accepted in the majority of cultures, I assume it isn't the case.)
Edit: Also if you're overweight and want to change that, or even just want to lose weight in general, it's probably a good idea to talk to your doctor about it and get advice from them. If you're willing to make some changes to your lifestyle, it's not *that* hard to lose weight. I know you aren't asking for weight loss advice, so only read the next part if you're interested.
My general recommendations would be: the only way to lose weight is to consume less calories than your body burns. One way to do that is to eat less, another way to do that is to burn more (exercise), you can also do both. The best way to keep track of how much you eat and eat less is to use a food scale to calculate calories, you can also use other methods but they are less accurate. I would calculate your BMR/TDEE (you can find tools to do this easily online) and then eat like 500 kcal less than that. A few other tips for eating less: if you drink sugary drinks, stop doing that. Drinking water can suppress appetite, and food high in fiber may be especially satiating. Also, another thing to note is that if you're weighing yourself a lot its normal for your weight to fluctuate a lot within a day, if you want to limit that you can make sure to do it at the same time/in the same situation every day. (if you always do it before you shower or when you wake up or after you have lunch or whatever, just keep it consistent if you want less variance).