I'm in the US, and as far as I know, tuna is ok every once in a while. "Although concerns have been raised about the level of mercury in any type of canned tuna, the FDA and EPA say pregnant women can safely eat up to 12 ounces (340 grams) a week or two average-sized portions of canned light tuna (limit albacore tuna and tuna steak to no more than 6 ounces or 170 grams a week)"
https://www.mayoclinic.com/health/pregnancy-nutrition/PR00109
The risk of listeria lies not in how fresh the deli meat is, nor the quality, preservatives, etc. Listeria is a disease that the ANIMAL itself may have. If you eat meat from a contaminated animal, then the risk to contract listeria is there. It does not matter how this meat was preserved. Cooking the meat kills the bacteria. The risk of it is low, but the consequences can be significant. Lots of pregnant women eat deli meat and are fine, but then there's the one who eats it ONCE and comes down with listeria. It's just a choice you have to make whether you want to risk it or not. It's important to note that signs of listeria typically present themselves a few months after exposure, so it's not a - i had deli meat last week and i'm fine - kind of deal. I've tried my best to stay away, but honestly I've had 2 or 3 cold sandwiches. I feel bad, and will feel like the world's worst mother if I come down with listeria, but man that craving was a hard one to get by! i literally refused to eat anything except a cold cut sandwich, anything else the thought made me gag.
Sorry, was babbling a bit. To the OP - If you don't want to heat up the meat, I suggest using leftover chicken for sandwiches! try going to allrecipes.com and looking up sandwich ideas. if you like veggies, try looking up vegetarian sandwiches?