At the moment the XA2 variants are the cheapest option with modern Android support (choose the form factor that suits you best). The 10 II is slightly more future-proof, since it has 64-bit support. There are no further supported models coming on short notice, so it’s a good moment to buy one. Sailfish support for the Xperia X is being phased out, so I would suggest to avoid it.
The dual-SIM version of the 10 II is supported: look for the codes XQAU51 or XQAU52 to be sure, but it’s going to be difficult to find an unsupported version.
You can save something compared to that offer: check https://www.idealo.at/preisvergleich/OffersOfProduct/200094929_-xperia-10-ii-sony.html .