The "no save point thing" is only really annoying if you're bad at remembering to bring Goho-Ms with you when you start dungeoning for the day.
If your goal is to make it through a dungeon in one day, realistically you use the vending machines every week(machine next to the item store sells TaP soda which restores 10 SP, can buy 5 a week, machine at end of shopping district sells three varieties of soda, all of which restore 5 SP, can buy 5 a week), and also buy a group of 3 Tiny Soul Tomatoes when you can(usually also once a week, restore 20 SP a use). Then you have the idea that chests respawn when you go up and down floors, so you can "grind" them as you grind levels, so you can get Snuff Souls(restore 50 SP a use).
Honestly, it's a LOT of work to do it for Yukiko's castle, and it really requires a good knowledge of what you're grinding for(usually a Slime to learn Resist Physical at lv7 and an Ukobach at lv7 that knows Resist Fire), and then fuse them into something that learns Media. Of course if you want to do all of this grinding it'll take you like 9 hours just to do Yukiko's castle by itself, so yeah...
As was said, you'll enjoy yourself a bit more just not following a guide for the first playthrough instead of doing all of these very gamey things.
Wait, wut?