YS-03 is worse as it doesn't have a manual mode. If you want TTL, you will need a converter with any strobe, but not every strobe is supported by TTL converters currently available on the market. TRT Electronics s-TURTLE currently supports Ikelite DS160, Inon Z240/Z330, Sea&Sea YS-D1, YS-D2 ,YS-D3, YS-110a, Subtronic Pro 160, Pro 270. OneUW, Isotta RED64, Retra PRO and Retra PRO X, UW-Technics converter supports Inon Z-330 / Z-240 / S-2000, Sea&Sea YS-D1 / YS-D2 (China) / YS-250, Ikelite DS161 /, DS160, Subtronic Pro-270 / Pro-160, Retra Pro.
The thing is, whereas built-in TTL support is common in land strobes, it is almost unheard of in underwater strobes. The only underwater strobes currently on the market with built-in TTL support that I know of are Seacam 160D, and they only support it with Canon and Nikon cameras. Older Seacams actually had separate SKUs for Canon and Nikon support, but the current model supports both. Basically, every major vendor (Canon, Nikon, Sony, Olympus/Panasonic) has their own TTL flash protocol, and the converter 'speaks' it and translates it into appropriate signals for the strobe in question. Different strobes have different discharge profiles, which the cameras are unaware of, and the converters account for that too.
Note that TRT Electronics don't list support for the original A7 cameras, only A7 II and up - I don't know if that's a simple omission, or if they really have a compatibility issue with a camera that old.
Also, keep in mind that low-power strobes such as YS-90 and YS-03 will really struggle to provide enough light to a full-frame camera in wide-angle scenarios - even if you get it working, you'll be largely restricted to macro.
What housing are you using? Do you have an optical or an electrical bulkhead, or both?