Even if u want a bigger sump above the DT I would try & fit a smaller second sump below the dt. It only has to be big enough for the return pump, ato & any water that would drain down when u turn the return off. Usually I want a long, shorter tank for the sump, but in your case a taller tank like a 20 H would work better. U can run it just deep enough for your return pump & have quite a bit of room for the extra water when the return pump turns off. If u run it at 7” deep that would be around 8 gallons, so it would leave u around 11 gallons of room. It would also make it to where u can run the dt at a normal water level. If not u would have to run the dt a little low to be able to handle the water from the sump when u turn the pump off.
I’m just using that as a example. Without knowing the sizes of your tanks we don’t know how much room u need. Otherwise your return pump & ATO would have to be in the DT.
If u decide to use only one sump then I would consider a external return pump. It still isn’t ideal but u wouldn’t have a return pump in your dt. If u have small tanks then u could figure out a way to somewhat hide a small pump in the dt.