As others have pointed out, Osaka does not have soaplands and opportunities for foreigners are limited, but the closest thing to a gaijin-friendly soapland will be Club Amour in Namba, near the Dotonbori.
If you're going to take the advice of those here and hit Tobita Shinchi, the nearest major station is Tennoji and that's where most of the bigger name hotels will be. However, in case you're traveling on the cheap, I just wanted to throw this out. The closest station to Tobita is Doubutsuen-Mae on the Midousuji (red) subway line. However, just next to that is the JR Shin-Imamiya station, and Shin-Imamiya has an abundance of very cheap budget hotels. Do a search on Booking.com and you'll see a number of options within a couple of minutes from the station, and from there you can either walk to Tennoji/Tobita (maybe fifteen minutes but a very easy walk) or catch the JR.
Personally, I won't stay in those budget hotels anymore (it was cool when I was in my 20s...not so much in my 40s) but I can personally vouch for Hotel Shin Imamiya. It was recently remodeled, has a nice lobby but bare bones rooms (resemble WWII dormitories) but I believe you can still get a single room for around 4k/night. There's a new bar in the lobby and they get tons of Asian/International visitors.
If you're willing to pay more for an interesting experience, Spa World Osaka (the largest onsen theme park in Kansai) has a hotel above it. I've never stayed there but Spa World is the only thing I enjoy doing when I'm back in town.
Otherwise, if you're looking for something more luxurious, you'll have plenty of options in Tennoji. Stay near a station on the Midosuji Line as that's the quickest way to get back into Shinsaibashi, Namba and Umeda. After you've blown your load you'll want to find good places to eat and drink and those are Osaka's hotspots.
FYI, I lived in Osaka for many years and the Tennoji area is considered the scumiest, nastiest neighborhood in Osaka city proper. It's not dangerous, but you'll see the dregs of the city if you walk around the area at night. Big homeless camp at the zoo, lots of vagrants roaming around and not the greatest manners. I don't mind it but it's definitely not where you'll want to take a date. Then again, since you're looking for places to blow a load I doubt that's going to be an issue.