Ireland might suffice. If the Irish Republic has been left in place then effective German opposition requires a limited action from Ulster but crossing Irish Sea will delay further response from Britain so a an invasion with a fast move inland could seize a large part of Ireland before a major defence could be mounted. Or, more economically, a major misinformation program backed by a trial landing/major raid. The Irish origin US population would be an easy feedback route.Invading Britain could be a diversion, or even a deception operation. Persuade Hitler to create a strong defense there at the expense of the French coast. A trans Atlantic invasion is a whole other level of difficulty, but if theres a relatively weak defense of Brittany...
The hard part of a western France invasion is the cross ocean logistic train. No UK stockpiling just a days sail away. The Free French need to be kept completely out of the loop given their OTL security habits. If Vichy still is in existence then they are either a security risk or a local armed disciplined asset in place depending upon your point of view. I can see no transport space being free to rearm them with US assets as IOTL. Also no UK based air assets to dominate the skies so German troops movement to, and on the battlefield will be far easier for them. The merchant vessel requirements will almost certainly suspend major amphibious activity in the Pacific. I presume that the war in the Soviet Union continues. The limiting factor is the shipping. Local air and naval superiority are possible around the landings so getting ashore, especially if Vichy assist, is a near certainly but the progress of the advance is a function of the regular shipping capacity. Given the fuel and land transport issues of Overlord IOTL and the fact that this timeline shipping takes many days, even weeks, to make a return journey, supplying a direct continental landing is only an option if the merchant etc. fleet is much larger than that employed in Overlord. On the other hand it is not being used to keep the UK going which will free some significant capacity. Even so, as I understand it, some part of Overlord stockpiling was to build up UK resources such that shipping could be temporarily diverted to Overlord. I am also aware that all this shipping requires somewhere to unload rapidly at all stages of tides and in most weathers.