What is the best Solo Rules or Rules for FULL Coop for LNoE?

[LabRat]

I just played Mice and Mystics last weekend, and I saw a mechanic that I've seen in other Cooperative games that may work in custom Solo rules for LNOE - an escalating threat meter. I've seen this mechanic in other games like Pandemic, and even ATOE has a similar mechanic in the form of the Shadow Track.

Basically, this is how the mechanic worked in Mice and Mystics:

1. During combat, dice are rolled when attacking and defending. The dice have a side that has a cheese icon - each time this shows up, a cheese token is placed on a timer of sorts.
2. When the timer fills up (has 8 cheese markers), the threat level moves up and the timer resets to zero.
3. Each threat level represents an increasingly difficult spawning method, for example (I don't own the game so I'm not sure how accurate this is):
Level 1 - 3 Rat Warriors
Level 2 - 5 Cockroaches
Level 3 - 1 Elite Rat Warrior, 2 Rat Warriors
Level 4 - 1 Cave Centipede
and so on

I don't have the idea fully fleshed-out yet, but here's what I've been considering:
1. The Zombie Outbreak meter would determine the following:
a. Number of zombies spawned - it doesn't have to be exact, but it has to be increasing per level. For example, at low levels the spawn would be 1d3, then 1d6, then 1d6+1d3, then 1d6 x 2.
b. Zombie types spawned - at higher levels, you can also spawn Zombie Heroes, Grave Dead, or even special custom zombies (maybe zombies with upgrades from Timber Peak?)
c. Number of Zombie cards that are put into play - at low levels, it can increase from 1 card, to 2, to 4, and so on.

What do you guys think?