You might start with your adult children. They are there at no cost, they know you and your stuff and if they are willing can be a big help.
If that isn't working, consider a Personal Organizer, such as...ME. I work as a nonjudgmental helper to keep you on track and getting the process to move along, with you always in charge of anything that gets ditched, donated, kept or sold.
An estate liquidator might be helpful if you have a lot that you want auctioned off. You will get pennies on the dollar, but it also someone else carrying the workload. I have used them and found it a great relief.
Senior Move Managers can help you if you are relocating and need someone to oversee the entire process from start to finish. Be sure to check references!! And, they aren't cheap!
Junk haulers bring a big truck and make all the trash items go away. You would need to have it all ready for them as they just take it and get rid of it at the landfill. Some people find this hard to actually watch their things leave, or you may find it freeing. Be sure to think it through.
These are ideas for major decluttering. I hope it gives you the keys to get started today.