I had the same question after being veg for 20 years, it took me a while to get the balance right, and yes, the freezer's definitely your friend!
I find that about 150g/5½ ounces liver is enough for me in a single serving, I can barely eat more after that because it's so rich, conversely anything UNDER about that weight of steak is just not enough, one lamb neck fillet (dunno size but it should be a fairly standard item) which I buy for the fats and connective tissue is just about enough for one meal, unless I pad it with some potato and carrots, in which case there'll be enough for a smaller supper.
I usually have some chicken or fish for supper (probably not a biggie for you) and with those I just have whatever the kind of "unit" size is, eg, a tin of tuna or chicken breast or leg, and pad it out from there if needed, because they come in all sizes and sometimes I have to go with what I can afford over what would be biggest. I don't know if you plan to eat pilchards (sardines) but I found that about 250g/9 ounces of those babies is enough for me, with some veg and the (moderately clean) tomato juice some british brands are packed in.
Most of my meals are heavy on the meat and lighter on veg but I've stretched meat by adding a small amount of rice to the casserole or crock-pot dish, and even lentils in the past, though I personally don't use them now. I've eaten other meats but those I've named all have different textures and so that's a guideline of what I eat, I'm a medium height woman and healthy weight (BMI wise, could lose a few vanity pounds) and in my 40's fwiw, bit more sedentary than I'd like due to practical reasons.
Maybe post an idea of your weight, age and activity level to get posts from guys closer to your body composition? My stuff's probably only useful to give you a rough idea of the minimums.
Good luck mate!