If you can keep the humidity up, and temperature down, during the day then pretty much anything except true shade lovers should do fine. We keep bromeliads, spider plants, Ficus species, Tradescantias, etc, in south-facing windows without major issues. If you look at gardens you'll see that most plants are actually happy, or even prefer, to grow in full sun. But (and this is quite a big caveat) this is assuming you can keep them moist and cool when the sun is baking, which will probably involve watering at least once a day during summer, otherwise the plants will struggle and you'll have the perfect conditions for red spider mites.
If running around with a watering can much of the summer doesn't appeal to you, there are plenty of succulents that would do well with more normal levels of maintenance. Cacti should thrive and if given a cold dry winter might even flower. Alternatively, if space permits, you could use bigger pots placed on the floor with larger plants in them, keeping the roots out of the worst of the sun, or go for semi-aquatic species like Cyperus that won't dry out as quickly if you fill the pot up to the brim.
Not all south-facing windows are the same level of sun - if you've got blinds or curtains or nearby trees then you'll have more diffuse light - but for the purposes of this question I'll assume you're talking about bright, hot, full sun!
Cacti will definitely do well, but if you've got pets, small children, or just don't fancy picking spines out of your hand when you brush against a cactus when drawing the curtains (ask me how I know...), there are a lot of other sun-tolerant plants that will be great for you!
Echeveria (aka 'Mexican Rose') come in a wonderful variety of colours, and have a powdery coating of farina which protects them from sun-scorch. They'll put out long flower spikes in bright light.
Hoya (aka 'Wax Plant') are a vining succulent and in bright light they'll do interesting things like new leaves coming in bright red before fading to green, or having an increasing number of silver splashes. When mature they'll put out heavily-scented clusters of flowers. I can't paste the pics due to formatting but there's a good set of images here
Other succulent names to look up: aloe vera (a classic easy-care succulent that can also be used in skincare and cooking), haworthia zebrina (pointy and stripy), haworthia obtusa (little translucent balls), pachyphytum oviferum (pastel and spherical), various forms of senecio (long strings and fluffy tails formed by small rounded leaves), crassula ovata (aka jade plant), sedum, and aeonium.
Oh, and while snake plants and ZZ plants are often recommended as low light plants, they're also absolutely fine in bright light too - they're super hardy and tolerate a very wide range of conditions.
In general I like to put succulents in my south-facing windows because I love succulents and keeping them anywhere else will often to lead to etiolation (stretched-out growth), and because they're most likely to avoid leaf scorch if there's a sudden heatwave. (I've had some lovely aroids scorched by the sun, so I'm speaking from experience!)
I actually freelance as a houseplant consultant - like a mix of a vet for plants and an interior designer / personal stylist for plants - and one of the things I really love doing is helping people find the right plants for them, taking into consideration their space, schedule, any pets/kids, access needs, etc. So if you (or anyone else reading) would be interested in some more personalised advice, do get in touch - I offer sliding scale rates
(Hope it's okay to mention that on here - I know employees of aquatic retailers aren't allowed to promote their stores, but there wasn't mention of freelancing - happy to have this part of my post removed if any admins feel it's crossed a line.)
Thanks for all the information you shared
A lot to think about
Yes the widows are full sun
No kids or animals ti worry about
Your chosen career sounds interesting
If you have a website etc im sure it would be ok to post it here as its not like you are spamming the blahblahblahblah and im sure others would like to see what you do
I have lots of chillies on my south facing window sill, and a peperomia angulata which I grew from a cutting. It's also where I start my seeds - herbs etc. I've found using bigger plant pots helps a lot with watering during heat waves, as do these terracotta vases which I use as mini olla pots. If you ever go on holiday during the summer make sure you take all your plants off the window sill or they're at high risk of drying out!