Here is the best strategy to finding treasure rooms, if you're not good at fighting:
Get the highest luck you can.
Get the most staircases you can.
Use staircases to go through as many floors as possible, hoping for treasure rooms.
Rinse and Repeat.
Some specifics:
Getting the Highest Luck you can:
In addition to checking the TV, looking for days where the Spirits are very happy, you'll want to have eaten food to raise your luck. The best options are, in order (and also order of difficulty), Magic Rock Candy, Lucky Lunch, Pumpkin Soup, or Spicy Eel. Lucky Lunch is probably the best you'll be able to do in large quantities, if you don't like fighting, but it also can take up to a year to put it all together since it requires Blue Jazz (from Spring), Tortillas from Corn (from Summer or Fall) and Sea Cucumbers (from Fall or Winter). Since you have barns and cows aplenty, if it's at the right time of year, you can put together a Bunch of Pumpkin Soup relatively easily, but it won't provide as high of a luck boost.
Note that there is a special late game item which I won't reference here which can make your recipes provide an even higher luck boost, and an item you can get from a secret note which also improves your luck. If you have access to these things you likely know what I'm talking about, if not I don't want to give spoilers unless you specifically ask for them.
Getting the most staircases you can:
There's three ways to get staircases. Money, Stone, or Jade. If you have stone, 99 stone can be turned into a staircase. If you don't have stone, Money can be turned into stone via Robin, and that in turn can be turned into a staircase. The cost on that is 9900. Both of those methods are quite expensive, from an overall resource standpoint, but they are options. Jade can be traded directly for a staircase via the Desert Trader. You can get a Jade every 2 days from a Crystalarium, so if you can get a few of those, you can get staircases rolling in pretty quickly. If you think about it, as long as you're using those staircases, a Crystalarium pumping out Jade is effectively producing 4,950 gold per day so they are Quite valuable in relation to this strategy.
Going through as many floors as possible, hoping for Treasure Rooms:
The Skull Cavern can be quite dangerous if you're not good at fighting, but that doesn't mean you need to just use staircases on *every floor*. If you want to conserve resources while playing it safe and avoiding fighting, your best bet is to see if there is a staircase you can get to without fighting which is already there, or if not, if there are a few rocks you can break hoping for a staircase without significant combat, and then if neither of those is the case, putting a staircase down. You can probably on a lucky day double the amount of floors you go through that way vs just diving straight down with staircases, and unless you have a TON of staircases they'll be your limiting factor, not time, anyway. To make this easier and more effective you really want to bring along some bombs, maybe 30-50 if you can afford them, though that represents 18000-30000 in costs (or 120-200 in Iron ore and 30-50 coal). So don't use a bomb to break 2 rocks, just use them on big clusters, again unless you're very rich.
Rinse and Repeat:
Blade can speak to whether or not the contents of a treasure room are predetermined for a given day, I suspect based on his quest they are not, as well as when and how the treasure room floors are determined. I don't have that information, my apologies. What I will say is that depending on your preferences and wealth level, since delving in the mines is not normally your thing, if you don't get it, you can restart the day and do something else instead, and preserve the staircases and bombs. That's if you're open to such things, just throwing it out there because while I delve in there quite regularly and as such build towards being able to have massive supplies of the above materials, I know that's not universally true. So it might be disheartening to use what might take a while to put together and not get it.
On average, it'll take 17 treasure rooms to find one. It's a 4% chance, and after 17 treasures you'll have found one 50% of the time. Keep in mind that random chance is random though, and 10% of people won't have found one after 56 treasures, so don't be discouraged if you don't find one right away, or even within the first 25. This is however much better than the available alternatives in my opinion, so I definitely think this method is the best option for your stated playstyle. Hope it helps!
