I would test this by starting from a copy of the contribute permission level. Scroll to bottom of Contribute permission level and click Copy permission Level, and give it a good name.
Of the 12 List permissions, 9 are checked.
It is highly likely you can clear the checkboxes for:
- Create Alerts
- Delete Versions
- View Versions
- Delete Items
Which leaves you 5 to experiment with:
- Add Items
- Edit Items
- View Items
- Open Items
- View Application Pages
7 of the 17 Site Permissions are checked. If you wanted to modify them you could start by leaving the 5 checkboxes on the Read permission level checked and start from there.
Another approach is to create a minimal permission level and use it in combination with the read permission level (assign both to a SP Group)
Keep us posted.
Greg