It's a bit late in the day as your son has clearly established himself as The Authority controlling you and your every movement, but... time to seriously start pushing back against his coercive control and interference in your life. It's not healthy for him or anyone around him to be allowed to continue in this manner.
Gently but firmly, bit by bit, stop acceding to his commands and demands. Maybe start by insisting on your choice of TV program. If that involves buying a new TV for your bedroom, do so. Tell him that you'll book the holiday when you're ready to. Small decisions that you stick to. Prepare for tantrums; stay firm and calm.
If there is some way you can get him to a therapist, please do. He sounds as though he needs outside professional support to deal with his feelings, whether they stem from insecurity, need to dominate, eruptive anger impulses or all combined.
Do you have any leverage, things he really wants to do for example, which you could use as a privilege which can be withdrawn? Some bargaining might be in order.
Please talk to your GP about your son's behaviour and see if you can be referred for free sessions with a counsellor to get support for yourself in developing strategies (CBT possibly?). Or if you can afford it, pay for sessions if the NHS is not viable (eg too long a wait).
Left to continue like this, your son will continue dominating you for many years to come and possibly escalate; if / when he does eventually find his own relationship, he'll likely be abusing and coercively controlling his partner.
If possible, get your other two DC on board with refusing to be abused and dominated by youngest DS. They must be pretty exhausted and fed up with his abusive behaviour. And is it remotely possible that he could spend some time with his father?
As for your new partner, do not be bullied into giving up that area of your life. It sounds as though your DC3 is seething with rage at your having any private life; but all parents deserve private lives - they are not slaves to their children. You do not have to be at his beck and call. If you give in and give up, your son will view it as a win. He'll repeat the behaviour again.
Switch off your phone when away. You can contact your other children by text from your partner's phone if you feel the need to check in. Just one or two check-i calls to DC3 should suffice while you are away. Your son needs encouragement to develop his own social life and to separate from you.
I think perhaps mixing up the times you and partner see one another might be a good idea so that your son doesn't develop a weekly build-up of rage as he waits for the weekend to come round. Perhaps invite your partner over more frequently during the week to have dinner, watch a show; or spend the evening out with him but be home to say goodnight to your DC3. Have him over for Sunday breakfast, for example. Make your partner a more integrated, fluid part of your life. Let your DC3 know he is not in charge and your partner is here to stay. That you are entitled to and seizing with both hands a private life and some adult pleasure.
Wishing you luck in this.