if you flip the motors you should have plenty of clearance as long as you run 83mm or larger wheels and 63mm motors. You’d have a bit more clearance w/ 50mm motors, which might let you go to 80mm kegels or 76mm flywheels if you are trying for super low.
I know you are in EU, so likely shipping and imports will kill the cost, but i still likd Daddie’s site for choosing new decks. Filter by some brands you like (or filter ones you don’t) and look for the drop through decks you like visually:
once you know a couple you like - then look at local skate shops or online skate shops in your country to speed and minimize import costs/fees/taxes.
You want flex though? That’s going to make it harder. Also be aware that some motor mounts may not clear the deck bottom at full lean, when mounted drop-through.
I know a Rayne Demonseed doesn’t clear the DIYes or Enertion mount even reversed. But that’s also a double drop.