There should be absolutely no issue with his secret service bodyguard and jail that isn’t just partisan politics. They’re not going to send him to the general population holding cells on Rikers. There’s a very good chance that a jail has already been prepared for him. It would be easy.
This is America. Every courtroom, every police station and outpost, most malls, some schools, and even a few public housing projects have a jail in them. The New York State government alone has 44 jails and prisons at its disposal, many of which have unused wings or even separate facilities already designed for high profile prisoners. Witness protection, politicians, rich-and/or-famous, they don’t go into general population. Private cells, solid security to keep unwanted and unauthorized out, even just a cell in one of the several courthouses already cleared by his Praetoriana, with the other prisoners removed to other facilities for the weekend or 30 days would do it.
In a worst case (for Trump, that is) scenario, they may have renovate and reactivate one of the (checks) 14 mothballed NYC jails currently not in operation but still owned and maintained by the state for a long term, secure (for everyone) confinement. Something tells me, though, that if that is ever determined to be necessary, they’ll find the money and make sure it happens.