Nas,
Welcome to the FOG!!!
In answer to your question, the 'vacuum' end of all the Festool hoses are all the same size, around 2". Wether it will fit directly to your vac depends on the exact diameter, but it will be very close.
Edit: I've just measured one of my hoses, and the dims of the 'vacuum' end connector are approx. 58mm external & 53mm internal:
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With regard to fitting the RO125 & TS55, the smaller 27mm diameter hose will fit both directly. Part number for that is either 452878 (3.5m) or 452880 (5m). Both those are anti-static. If you want the cheaper non-antistatic versions, the numbers are 452877 and 452879 respectively.
Having the antistatic hose will not give you any benefit over the non-AS hose with your standard shop vac; however if you intend to purchase a Festool vac in the future it may be better to purchase an AS hose now. That's entirely your choice.
Alternatively, you could go for one of the slightly larger 36mm diameter hoses - this I think fits over the TS55 outlet rather than inside it, and you'd need a reducing adaptor to fit it to the RO125. Again, I'm not certain of this as I only have the D27 hoses - I'm sure another member can confirm or deny this conclusively.
HTH,
JRB