"Disassemble" HTML

For an existing project I want to change my editor from TinyMCE to EditorJS. Creating new content works fine already. But I have around 2k "old" entries I need to convert to the new format. Basically, TinyMCE stores the full HTML source with <div> and all that.

EditorJS stores cleaner JSON, like this, which allows me to parse the elements the way I want to.

This is an example on now the new data is stored in the database:

{
	"time": 1646670246973,
	"blocks": [
		{
			"id": "lyez4SLqIO",
			"data": {
				"text": "This is a test"
			},
			"type": "paragraph"
		},
		{
			"id": "S41StgWZCx",
			"data": {
				"text": "Headline One",
				"level": 3
			},
			"type": "header"
		},
		{
			"id": "5m84NVRPuJ",
			"data": {
				"text": "More text..."
			},
			"type": "paragraph"
		}
	],
	"version": "2.23.2"
}

Like I said, I have lots of old data that looks like this:

<div><p>adsfdsfadsfdsfadf</p></div>
<div><p><img src="https://cdn.example.com/85da5087-a5e3-40f7-aa8d-2cfa23cab329/attachments/screen-5_1645774964.png" alt="" width="790" height="444" /></p></div>

It's usually much more content and a bit more complex, including iframes and stuff. What would be the best way to convert the old, standard HTML to the new format?

This is my starting point right now. My problem now is how to get data for $bodyBlocks?

$body = $submission->body;
$blocks = [];

foreach ($bodyBlocks as $item) {
    $blocks[] = [
        'id' => 'lyez4SLqIO',
        'data' => [
            'text' => 'Headline One',
            'level' => 3,
        ],
        'type' => 'headline'
    ];
}

$submission->json = [
    'time' => now(),
    'blocks' => $blocks,
    'version' => '2.23.2'
];

$submission->save();