For me I would repeat Moissac to Eauze.
Michelin map/guide 161 Chemins de Compostelle has five relatively easy stages for around 120 km
Another two stages totalling 50 km would get you to Aire-sur-l'Adour.
At Moissac I strongly recommend the gite
La Petite Lumiere with a communal meal and marvellous hostess.
At Larresingle I suggest
La halte de Larresingle. This is about 600 m on the other side (south) of the village. Another communal meal.
From here to Gondrin (I know, it is not on the GR 65. But neither was Larresingle) is the marvellous Voie verte de l'Armagnac. A former railway you are in sub-tropical bush (forest) for about 8 km. And there is no doubt you have entered a part of France where rugby rules.
At Eauze you could not do better than
La grange de Marie-France and I strongly suggest the demi-pension. Marie-France is a marvellous preparer of meals and a bon vivant to boot. And not forgetting her l'Armagnac presenattion and tasting. And the wonerful (for me at least) the Museum just east of the "cathedral" with a treasure trove (literally) of Roman coins, jewellery and artefacts.
And finally at Aire-sur-l'Adour the (again for me) the fascinating
gite Urseline Chapel on the GR65 heading south west with a communal meal (demi-pension).
@CJW , I hope your proposed meander provides lots to see and enjoy. Kia kaha (take care, be strong, get going)