I've lurked while various comments have been made: Have you considered installing skirting-board radiators? These are:- long, not very high (about 9 inches); only protrude into a room by 2 inches; can be 'interrupted' where doors into eve-storage doors are extant; can be fitted with TRVs; etc. etc. Lots of armchair sceptics will scoff - but, so what?