I'll address this in parts. In terms of phrasing, you're a bit off from something I'd expect to see in officially published material. Try something like this:
When you cast a spell that targets one or more creatures using a spell
slot of a higher level, you may use your reaction to make one weapon
attack against a creature that was a target of the spell. If you do, you cast the spell at one level lower than the expended slot.
That said, this is really weird. I'm not aware of any abilities (non-UA, anyway) that let you spend your reaction proactively like this. Much more common would be using a bonus action, a la Shield Master. But you don't want to use the bonus action, so we need to look for a different example. How 'bout College of Swords bard flourishes? That'd change the wording to something like this.
Whenever you cast a spell on your turn that targets one or more
creatures using a spell slot, you may make one weapon attack against a
target of the spell as part of that action. If you do, cast the spell
one level lower than the expended slot, and you can't take reactions
until the start of your next turn. A spell's level must be lower than
the level of the expended slot in order to make use of this ability.
Still have the penalty, but without all the janky weirdness involved with using a reaction proactively. (This way is admittedly slightly better, since one could conceivably use their reaction and then make use of this ability, but that's an extreme case I don't think often enough to be worth extra verbiage.
And then the second half becomes again (no need for alternatively. This isn't an alternative -- it's a completely different situation):
Whenever you cast a cantrip targeting one creature, you can expend one
spell slot to make a weapon attack against the target of that spell.
If you do, you can't take reactions until the start of your next turn.
