Ruling on wearing ordinary clothing over the izaar and rida’ [ihram garments] before starting the rituals
Question

                I am going to travel for ‘umrah next week – in sha Allah – and I intend to enter ihram from my house in Cairo, because it is difficult to do ghusl and change my clothes when passing the miqaat in the plane. But the weather is cold, and wearing the ihram garments that are relatively light may cause me to become sick en route to the airport, especially since my immune system is weakened due to the chemotherapy that I am undergoing.

Can I start the steps of ihram at home by doing ghusl, putting on perfume, wearing the ihram garments and praying, but deferring saying “Labbayka ‘umratan (Here I am for ‘Umrah)” and reciting the Talbiyah, then put on warm tailored garments over the ihram, then take off the tailored garments and say “Labbayka ‘umratan” and the Talbiyah later on, in the airport or on board the plane? This is so that I will not put on any tailored garments after completing the first steps of entering ihram.
Praise be to Allah.
      It is permissible for the one who wants 
      to do Hajj or ‘umrah to do ghusl, put on perfume and whatever garments he 
      wishes over the ihram garments, and to do any of the things that are 
      prohibited when in ihram, so long as he has not formed the intention to 
      actually begin the rituals. This is indicated by the report narrated by 
      an-Nasaa’i from ‘Aa’ishah (may Allah be pleased with her), who said: I put 
      perfume on the Messenger of Allah (blessings and peace of Allah be upon 
      him) with my own hand, when he entered ihram – when he wanted to enter 
      ihram (and before he did so) – and when he exited ihram – before he 
      completely exited ihram (in the case of Hajj). Classed as saheeh by Shaykh 
      al-Albaani (may Allah have mercy on him) in Saheeh Sunan an-Nasaa’i. 

    Al-Haafiz Ibn Hajar (may Allah have mercy 
    on him) said:

    This report is quoted as evidence that it 
    is mustahabb (encouraged) to put on perfume when wanting to enter ihram, and 
    that it is permissible to leave is there after entering ihram, and that it 
    does not matter if its colour or fragrance remain; rather what is prohibited 
    is to put it on anew when in ihram. This is the view of the majority of 
    scholars.

    End quote from Fath al-Baari 
    (3/390) 

    Shaykh Ibn Baaz (may 
    Allah have mercy on him) said: There is nothing wrong with doing ghusl, 
    putting on the ihram garments and putting on perfume at home, because they 
    are close to the miqaat by means of vehicles. But what is prescribed for 
    them is not to enter ihram except at the miqaat. Ihram means forming the 
    intention to begin the rituals. This is what ihram means. Then it is 
    prescribed for them when forming the intention to utter the ritual intended, 
    so one should say: “Labbayka ‘umratan (Here I am for ‘umrah)” or “Labbayka 
    Hajjan (Here I am for Hajj).”

    End quote from Majmoo‘ Fataawa Ibn Baaz 
    (17/52) 

    Shaykh Ibn 
    ‘Uthaymeen (may Allah have mercy on him) said in ash-Sharh al-Mumti‘ 
    (7/69): The words “his intention is a condition” refer to the intention to 
    begin the rituals, i.e., forming the intention to begin the rituals is a 
    condition; it is essential to form the intention to begin the rituals. If a 
    person recites the Talbiyah without intending to start the rituals, then he 
    does not enter ihram merely by reciting the Talbiyah. If he puts on the 
    ihram garments without intending to begin the rituals, then he has not 
    entered ihram just by wearing the ihram garments. The Talbiyah may be 
    recited by the pilgrim and others, and wearing the izaar and rida’ is for 
    the pilgrim in ihram and others. End quote 

    Based on that, it is permissible for you 
    to wear tailored clothes, and to wear whatever you want, to protect yourself 
    from cold, over the ihram garments (the izar and rida’), and to do 
    everything that the person who is not in ihram does, of the things that are 
    prohibited whilst in ihram, even if you have done ghusl and put on the ihram 
    garments in your home, so long as you have not formed the intention to begin 
    the rituals. This intention – as stated above – is an essential condition, 
    but it does not have to be done until you come in line with the miqaat. It 
    is permissible to enter ihram before reaching the miqaat, but this is 
    contrary to what is preferred. 

    And Allah knows best.