Reasonable, with two or three obvious gaps

Nothing here is alarming, but your answers point at specific losses rather than a general problem — which is good news, because specific losses are cheap to fix.

Draught-proofing is where to start. Sealing gaps that exist by accident costs very little and addresses the faster of the two ways heat leaves a house. Insulation addresses the slower one and costs thousands.

Check the loft hatch and any unused chimney before spending money on anything larger.