This might be a lot to take in, but your post is lacking in a few crucial details so I want to cover my bases as this is not a back-and-forth. I will summarize at the bottom.
There are really a lot of options in terms of both mods and tanks, but especially mods. Because you want battery life, you might want to consider a single or dual-18650 mod that is capable of more power than you need and simply using it where you want. This is a sure way to get more battery life from your mod, but there are also compact, middle power options that will do what you need and whose charges should still last for a while. Battery life is also less of a big deal with replaceable cells, both in terms of switching them out and having a certain degree of flexibility with your milliamp hours vs. continuous discharge.
First of all, if you are someone who is content using the exact same set-up all the time, there are at least a couple of "all-in-one" devices you might consider. The Aspire Plato and Kanger NeBox come to mind. They both use a replaceable 18650 battery. The former does 50W and the latter does 60W. They both have temperature control for nickel and Titanium, if you decide you want it. The Plato kit tank is 5.6mL and the Nebox tank is 10mL. The Plato has adjustable airflow, the Nebox doesn't. Both are compatible with a few different types of coils and both run around $48-60.
As for mods, again there are really so many options but I'll reel it in. Tesla Nano 60W or 100W would both be a good choice, IMO. Yes, I realize 100W is about 3x more than you need, but both are small and inexpensive and at 30W, the 4500mAh battery in the 100W nano will last you quite a while. However, the 60W has large capacity battery, too, and may be more your style. Besides those, there is the recently-released iStick Pico and the staple EVic VTC Mini. Those both use replaceable single 18650s, both have more than sufficient power, and again both have temperature control. All of these devices are relatively inexpensive, but well made. There are so many options but I do think any of the above (including if you decide on an all-in one) would do the trick.
I mostly rebuild so I'm less up on subohm tanks these days and it's really kind of a popularity contest, but I can still recommend one or two. I really enjoyed Eleaf's Melo 2 and am enjoying the new Melo 3, added bonus for you is that the coils they use are compatible with the Atlantis 2 and vice versa IIRC. Both are top fill. Melo 2 is 4.5mL (I think) and the larger Melo 3 is 4mL. The other benefit is I think that both are good at the wattages you like, whereas some tanks only use extremely low resistance coils that are really meant for higher power. Again, for the wattages you like I would also maybe consider a Kanger Toptank (mini). You will easily be able to find coils that fit your style for that, as well.
If I had to choose one of the above to recommend for you: I would probably go with the Tesla 60W nano and pair it with the 4mL Melo 3 or the TopTank.
If you get a device with a replaceable 18650, at the power you like to vape right now you can use a 20A battery. I would recommend LG HG2's with their 3000mAh capacity. I also like Samsung 25Rs (2500mAh). If you suddenly decide you need to start vaping at 180W and .1ohm, that's a different discussion entirely.
Please feel free to PM if this is too overwhelming or if I took a swing and a miss with the mod search.
