Minecraft multiple Mob data tags
Solution 1:
Here is the wiki on slime data values. Maximum size is 3 naturally. Size has to be capitalized in data tag and Health can be used as well.
Here is the command:
/summon slime ~ ~ ~ {Health:1,Size:3}
Edit: Response to comment
I played with Attributes to set maxHealth but it did not appear to work. After your comment I did some research.
I found this post on a forum which talked about how Size tag overrides the Attributes. It also points to MC-33285 bug report which states that summoning slimes with maxHealth doesn't work.