Hello.
F11's resident sambo guy here.
I'm combat sambo a useful way is to step off center after a jab and throw what appears to be a wide right/left hand. What it actually is a cover to wrap your arm around their neck and pull them off balance, as their weight shifts onto one leg, you Osoto gari them to sweep.
You can't really strike into an ouchi gari though, as you generally need to be clinched in order to pull it off. What you really want to do is look at how Ronda Rousey does it.
You can shift the weight with your left hook (assuming orthodox) in order to push them towards the reaping leg with more momentum but it could be difficult to hook it in off of the left hook, it might be better to throw a left hook while in the clinch.
Generally you need to transfer weight in the same way you would when throwing punches. You bring your weight to one side to grant more power when you attack from the otherside, a left hook will load your body in a way that you can get more power when you shove them with the underhook.
I'd also say if you're talking about MMA, train your throws all the time with and without gi, for versatility but when looking at application of throws watch less gi judo and more Ronda Rousey, Khabib Nurmagomedov, Fedor Emelianenko and Sexyama.