One of the easiest rta's I've used is the ehpro bachelor. Runs around $30 from the u.s. most places or around $20 from china if you don't mind waiting a few weeks for shipping. Comes in 2 versions, a taller bachelor with 4ml capacity and shorter bachelor nano with 2ml capacity. They're 22mm tanks so should fit fine without hanging over the sides of the ipower mod. Both are single coil and they're 'postless' decks.
No tails from the coils sticking out the other side of a post, getting caught in the wick or potentially hitting the side of the chamber walls. The ends of the coil slide down into two holes until they bottom out then a small hex screw on either side tightens them up. Another perk is the way they wick. There are 2 slots in the wall of the deck at either end of the coil. Roll the cotton up, slide it through the coil and snip just past either side of the deck wall. No fluffing, no odd angular cuts to the wick tails, no tucking.
The juice flow opens up when the tank is fully screwed down to the deck, when unscrewing the tank the first thing that happens is the juice flow closes. You can remove a full tank and set it on a table or counter without it spilling in the event you want to change the wick or put a different coil in, make adjustments or whatever. No need to run the tank dry or dump it out.
I'm not sure how it compares to the tank you've been using for airflow, the bachelor is more what I'd call a moderately restricted direct lung inhale. It's not like mtl tanks but not as wide open as others. Not a cloud beast so if that's what you're looking for it won't be a great fit. Still produces sizable clouds but it has good flavor. If there's any downfalls, it can leak a little. By that I mean the top swings open to fill it and swings closed so there's a silicone gasket at the top. It doesn't screw shut. I could lay it on its side and leave it that way overnight on a regular basis with no puddles but every now and then there might be a single drop of juice around the top where the lid swings closed. Not like running down the tank or anything.
Seriously hard to screw it up, if anyone could I probably would have. The only other leaking issues I had were running coils too small in diameter and not using enough cotton. Seems to work best with 3.5mm to 4mm diameter coils. I used a 16d (16 penny) nail to wrap my coil wire around for several months before getting a coil jig. It forms a coil around 4.2mm and works well. I opted to get a coilmaster v4 jig set, runs around $17 on amazon or $11 from fasttech (china). They also have a cheaper one that's almost the same, the v3 for around $7 from china. Seems the only difference is the silicone holder for the coil rods in the v4, otherwise they look to have the same pieces.
A jig isn't necessary, just makes the coil winding easier and more consistent. Most wires can be had for a couple dollars per spool, I've never used anything fancy just ud/youde wire. Personally I tend to use 26g ss316L the most, works in both temp control and wattage mode. A single spool is usually 30ft of wire, enough for anywhere from 2-4 dozen coils depending if you twist them or not (2 pieces twisted together) for around $2-3 depending where you buy from. Something like muji organic cotton pads off amazon run $6-8 a bag for 60mm x 50mm pads (140 count). Each pad's good for 4-8 wicks. $10 worth of cotton and wire and you've got wicked coils enough to last you a year or better even if you rewick every day.
Juice is subjective based on flavor preferences. Some inexpensive places to check (u.s. based, not sure where you're from), verde valley vapes, broke dick ejuice, vapewild, mt baker vapor, the sauce la, vape moar. I'm sure there are others but those are off the top of my head. Not all are winning flavors (just being honest) but same goes for premium ejuice as well. Just as a quick comparison, a premium company like halo sells ejuice in 30ml bottles for $22. 30ml of vapewild juice runs around $7 for 30ml or less if you buy more. For instance if you buy 4 bottles (120ml) it drops to $5 for a 30ml bottle. 4x the juice for the price of halo. Vape moar sells 132ml for $20. Broke dick sells 2x 120ml bottles for $22. Depending where you shop the same $20 can get you anywhere from 30ml to 240ml of juice.
Hopefully some of that helps, it's info I didn't have right off when I started vaping. Finding good tasting ejuice is a personal journey. There are less expensive options though for both juices and wicks/coils. I was a 2pk a day smoker and smoking an inexpensive brand in literally the cheapest of all 50 states for tobacco. Vaping is easily cheaper for me so I know it can be for anyone else in the states. I'd have to vape 30ml or more a day to get close to matching or exceeding the cost of smoking (not including poor health when smoking).