You could ask, but generally oxygen is prescribed for low oxygen saturations at rest checked via an arterial blood gas sample. They can not prescribe oxygen based on a sat probe or Capillary blood gas as these are inaccurate. If your husbands oxygen is below 88% (BTS guidelines), supplementary oxygen is required.
As previously mentioned, if your husband experiences breathlessness on exertion, dependant on what he desaturates to and how long it takes to recover, he may benefit from short burst oxygen which can be delivered by face mask or nasal cannulae.
From what you have mentioned and his activity levels prior and after infection, he may benefit from nebuliser therapy when he has an infection. Nebulisers enable a higher dose of atrovent(salbutamol) and iprotropium bromide which helps to open the airways and reduce inflammation, enabling effective breathing.
With chest infection it is expected to be breathless with his condition as the infection interferes with the gas exchange at the alveoli, but with antibiotics and nebulised therapy this should help with the breathlessness.
Your best bet, is to ask the consultant for a oxygen assessment. Your husband may benefit from being seen by a community matron who helps people with long term conditions and can instigate oxygen when they feel it necessary, It also gives you an extra contact point when you are concerned with anything. Your Gp can refer you.
Also, before I go, does your husband use a spacer for his spray inhalers? These enable a more accurate dose being inhaled and ensure the breathing technique is correct for an accurate dose and benefit.
Hope this helps