a corner of the poly tunnel cordoned off with poly styrene sheets and racking in
on cold nights the lid goes on and an old quilt thrown over that and a small thermostatic heater goes in on a frost free setting
Have you tried sowing a Tomato in March and seeing what difference it makes?
A couple of chums of mine did an experiment last year sowing some early, and some in March, and I think they had less than a week's cropping from the early ones before the later ones started, and they decided it wasn't worth the hassle of nurturing the earlier sown ones. You might also find that the later sown ones are more robust, healthy, plants having had less/no stress when young.
I can understand wanting to make a start ... so maybe half-and-half this year?
I used to plant Potatoes at the earliest possible date, to get an early crop. I'd be out there carefully earthing up on frosty nights, sometimes with a torch if the weather caught me by surprise ... and in years with a late frost I would have to have lawn mowings that I could heap on the, by then large, early potato plants. Lots of fleece to put over the rows ...
Well Blow That! I haven't done it for years. I now grow some bags / containers for the number of spuds we will actually eat early, I plant just a few earlies to then provide meals for a couple of weeks, and then plant the rest at a date where there is no chance that I will have to do anything more than regular earthing up to keep the frost off them. Similar approach with early sowings of Veg