Hello!
As others have pointed out, you'll need a full 5mm wetsuit minimum.
Ras Mohammed and Tiran offer the best sites within reach of Sharm via day boats. The wreck of the Thistlegorm is a longer journey requiring a very early start and it's typically only offered when enough divers are interested. If diving this wreck is on your bucket list, I'd contact Sinai Blues and enquire before your trip. If they have no scheduled Thistlegorm dates and it's an absolute must for you, you'll still have time to talk to other operators.
While I have no personal experience of them, I believe Sinai Blues operate some of the fastest RIBs in Sharm which allows them to offer single-tank dives to Tiran, for example. Or so I've heard.
They probably expect divers to kit up before setting off. For 2-tank dives, there'll probably be a surface interval spent on the RIB and the wind-chill factor might be a nuisance. It wouldn't surprise me if some dove in dry suits. Definitely pack a good hat.
A warm fleece will likely be necessary in the evening. This is the desert and it still gets chilly in April once the sun has set.
Enjoy your trip!