You are restricted to the cantrip
The PHB has the following rule:
If a specific rule contradicts a general rule, the specific rule wins.
I emphasise this, not because there is a general vs specific conflict, but instead to reenforce how we should interpret the rules.
The general rule for casting a spell (from the PHB) states:
When a character casts a spell, he or she expends a slot of that spell's level or higher, effectively "filling" a slot with the spell.
The general rules don't provide for a difference between attempting to cast a spell, and casting a spell. Thus the salient mechanic of casting a spell is the expenditure of a spell slot.
Counterspell is a specific rule that modifies how a spell is cast. As such we have to assume that the general rule (ie that you have cast the spell) still applies, unless Counterspell specifically modifies it.
The relevant text of Counterspell is (emphasis mine):
You attempt to interrupt a creature in the process of casting a spell.
If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect.
On a success, the creature's spell fails and has no effect.
The specific rule of Counterspell says that the spell fails and has no effect. Importantly it does not say that the casting of the spell is undone (or some other variant of this).
The plain reading of something failing is that an action is performed but it doesn't succeed. The action is not reversed, it fails to succeed.
It also specifically says that the creature is casting a spell.
Additionally the casting time specifies when you can take the reaction to cast Counterspell:
1 reaction, which you take when you see a creature within 60 feet of you casting a spell
You don't prevent it from casting the spell. In other words you don't preempt the casting, you cause their casting to fail instead, by interrupting some vital portion of the spell.
To put it up another way, Counterspell modifies the result, not the initiating action. In particular it does not give the original caster their spell slot back.
So, you have cast a spell as a bonus action, but the spell failed. Thus the rules surrounding casting a bonus action spell apply. In particular the other spell you cast must be a cantrip.