If you're running a foot-slogging list, shoota boys are your friend. Slugga boys belong inside vehicles. In fact, I think you should convert your slugga boy mobs into shoota boys. In 5th edition, the shoota boy is the most efficient point purchase across all
40k.
Think on that - for 6 points...SIX POINTS....you get an infantry model with an assault 2 STR4 gun, who is WS4, STR4, T4 on the charge. In terms of math hammer between shoota and slugga boys, it's pretty simple. Slugga boys have +1 attack in close combat, and shoota boys have +1 attack outside of close combat. Since your Orks on the assault are only I3, you're going to strike last meaning that 30 boyz are going to take some casualties before getting their attacks back.
On the flip side, shoota boys get 2 shots before assaulting, and the enemy doesn't get to shoot back first and cause casualties - putting in any kind of hurt before you assault is incredibly valuable. And since it has an 18" range, you can shoot into a unit even when you don't have range to assault this turn. My advice for green tide:
Take all your troops choices as shoota boys. Consider taking a squad of gretchin - you can spread them across your front lines to provide 4+ cover saves for your whole army. Alternatively, you can take a squad of ork boyz to do the same. If you make them 'Ard Boyz they gain considerably in staying power.
Want to get real freaky? Take a squad of 'Ard Boyz, stick Mad Dok Grotsnik with them for a 4+/4+. Spread that unit out 2+ coherence to minimize the damage that blast templates can do, and have the whole thing move+run in front of your army. Your screening unit has 4+ armor saves, 4+ feel no pain, and the rest of your army has 4+ cover saves now. If your points allow it, what really tops off the list is adding some fast attack Stormboyz. You can put them into close combat, or have them multi-assault to shake/stun some tanks/artillery, have them get in fast and tie up enemy units (hello Tau!), or if the situation doesn't call for it, you can leave them behind your screening unit and keep them in reserve to get in where you need supporting assault units at.