beefing up a small beer

I am planning a partigyle brew this weekend with the following stats

Grain bill

10lbs ‘mild’ malt (actually pale malt re-kilned at 230 for 2 hours)

mash at 148-150 for 1 hour

first runnings will be 1 gallon of 1.105 XXX mild with 1 oz of goldings at 240 minutes
second runnings (and here is the question) will be 2-3 gallons of small mild but with that low a mash temp I expect it would be to thin so I am thinking I will cap the mash with a little something. But what? Oats? crystal? Rye? any and all ideas welcome. Just be aware that the goal is more body. I figure I will bring the ‘sparge’ water up to a temp sufficient to hit around 158 on the second stage of the mash.

Hops for the small beer will also be goldings, havn’t decided on amount yet though, probably lots of late hops (I have 6 oz for both beers).

Also planning on using 1968 ESB yeast for the XXX not sureif I want the same for the small beer or to try something else. ideas welcome here as well.

Quick question: after a 4 hour boil, how much wort will be left if you start with one gallon first runnings?
I’d cap with some light munich malt.  I love munich malt.

1 gallon is post boil volume. preboil volume will be about 4 gallons. hmm, munich it’s a thought.

flaked barley? carapils? flaked oats?

yeah I am leaning towards a little crystal malt. either cap the mash or just steep the crystal separatly and add to the boil.