Want to replace mdadm raid (with only 1 working drive left) with a new single - non raid drive

I setup a brand new system a few months ago and chose to make it use a RAID. That consisted of a boot drive, and two identical drives for the raid.

The second of the identical raid drives died, so now my system is basically a single drive raid.

I want to move to keeping the boot drive (sda1) but replacing the other drive with a solid state drive.

My problem is that I just don't understand how the raid works and what is stored where.

This is what I have left:

Disk /dev/sdb: 931.53 GiB, 1000204886016 bytes, 1953525168 sectors Disk model: TOSHIBA DT01ACA1 Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes

Disk /dev/sda: 931.53 GiB, 1000204886016 bytes, 1953525168 sectors Disk model: Hitachi HDT72101 Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: D44AD34E-AE8F-452A-A6B8-67950F5F2954

Device Start End Sectors Size Type /dev/sda1 2048 1050623 1048576 512M EFI System

Disk /dev/md0: 931.4 GiB, 1000069595136 bytes, 1953260928 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disklabel type: gpt Disk identifier: 85A80476-09FF-4D7C-8205-3289F645CA69

Device Start End Sectors Size Type /dev/md0p1 2048 1953253375 1953251328 931.4G Linux filesystem

My assumptions are

1. /dev/sda1 is a disk on its own, handling booting
2. /dev/sdb is the one remaining functional drive from the raid
3. /dev/md0 is some sort of "shadow" drive that represents the now (1) disk wide raid, using /dev/sdb only now since the other drive died

This is the mdadm query result:

drool@rolath2:/home/felinicity/server$ sudo mdadm --query --detail /dev/md0 [sudo] password for drool: /dev/md0: Version : 1.2 Creation Time : Mon Jan 31 16:37:22 2022 Raid Level : raid1 Array Size : 976630464 (931.39 GiB 1000.07 GB) Used Dev Size : 976630464 (931.39 GiB 1000.07 GB) Raid Devices : 2 Total Devices : 1 Persistence : Superblock is persistent

 Intent Bitmap : Internal

   Update Time : Tue Nov 15 18:00:48 2022
         State : clean, degraded
Active Devices : 1

Working Devices : 1 Failed Devices : 0 Spare Devices : 0

Consistency Policy : bitmap

          Name : ubuntu-server:0
          UUID : 2325d27a:bc0c11b5:9e1c5b30:0647ee03
        Events : 31895

Number   Major   Minor   RaidDevice State
   0       8       16        0      active sync   /dev/sdb
   -       0        0        1      removed

What is my easiest path toward using a solid state drive for either everything, or just to replace /dev/sdb and keep all the data on /dev/sdd?

I'm not against keeping the boot drive, staying with a 1 drive raid (which seems dumb), or adding a new larger SSDs and letting raid populate them and then removing the non-SSD drive.

I just dont want to build and install all the crap I've already loaded.